Thank you for your interest in the Yo2. The topic of the hole design has come up a number of times. Rather than reinventing the wheel, here's a post I made shortly after the knife was released that explains more detail about the logic of the design process:
Thank you all for your comments and enthusiasm regarding the Yo2. I am very pleased to have it in production and I'm thrilled at the way it turned out.
I wanted to share a couple of fine points regarding the design. Like everything else I do, I like to explain why. You are free to agree or disagree, like or not like, but at least you'll have the information to make a decision.
With regard to the not-fully-exposed Spyderco hole, I wrestled with various options on this during the design. I did not want to do the large index-finger choil of the original Yo because it narrows the grip too much in that area and starts to force the hand into a saber grip. The goal was to keep the closed knife as narrow as possible to preserve access to the pocket.
I had a similar challenge when I designed the Be-Wharned. One thing that I learned during that process was that the natural hand position for a thumb opening is typically not with the plane of the handle completely flat. Most people naturally hold the knife palm up, but with the knuckles at about a 45-60-degree angle to vertical. That means that your thumb also indexes the hole (or stud) at an angle, not flat on top of it. With the Be-Wharned, holding the knife at this natural angle and driving the thumb straight along the chamfer of the handle produces the most positive, reliable, and comfortable opening.
With that experience as a guide, I focused on the functional part of the Spyderco hole. When the closed knife is viewed with the edge down, tip to the left, this section is from 12 to 3 o'clock. That's where the thumb actually bites and drives. That part of the hole is completely unobstructed.
As for the lock release cutout, I purposely made it smaller than that of the Para2. There are two reasons for this: First, some users--especially those who grip the handle tightly with their index fingers during opening--get a slight pinch from Compression Locks as the blade is opened. This is caused by the liner moving into the G-10 scale as the blade clears the detent ball. To mitigate this effect, I asked that the top of the Compression Lock tab be recessed slightly below the top edge of the G-10 scale and purposely made the recess smaller.
Second, speed closing of the knife is not high on my priority list. I close the knife by pinching the lock between my thumb (on the G-10 scale) and the nail of my index finger (on the lock tab). I can do this (and have done it) all day long without soreness or fatigue. For me, it's perfect the way it is. Most importantly, the knife closes exactly when I want it to and I still enjoy both the extreme strength and the I-don't-need-to-put-my-fingers-in-the-path-of-the-edge safety of one-handed closing.
I chose the standard hourglass clip for the Yo2 because it has been refined and perfected over the years. It works great, so why reinvent the wheel? Also, savvy Spyderco fans know that the same basic clip design used on the Yo2 is used on the Endura and Delica, but in black (and with the addition of the lanyard hole that matches the holes in those knives). Don't like the shiny clip on the Yo2? Buy a replacement clip for an Endura for a few bucks and you've got an instant subdued clip. How easy is that?
As far as clip position goes, most folks know I prefer tip-up carry. The key to getting a personal defense knife into action quickly is being able to draw it and immediately open it without having to change grip position. The key to that is making sure that the overall size of the closed knife, the position of the Spyderco hole, and the height of carry are all proportionate to the average hand size. If you have a big knife with a deep-pocket clip, it may carry discreetly, but when you draw it you're holding it by the butt end with your thumb a long way from the hole. Unless you can magically Viagra your thumb into growing, you have to change your grip to get the knife open.
The clip placement on the Yo2 makes the knife ride high enough so that, with a proper draw, your thumb is automatically on the opening hole when the knife clears the pocket.
If you prefer discretion and a low profile over deployment speed, I purposely added tip-down carry to the Yo2. The clip holes at the pivot-pin end of the handle are as close to the front edge of the handle as physically possible to support deep-pocket carry. Yes, it's tip down, which is slower. So is deep pocket carry in general. If you need deep-pocket carry and speed, carry tip down and use a Spyder-Drop opening. You'll find that although a small portion of the Spyder Hole is obscured, there's still plenty of surface area to grab onto. As you pinch the hole with your thumb and index finger, you'll also find that your fingertips start to push the handle away from the blade, "cheating" your start on the opening.
As for a lanyard hole, I'm not a fan of fobs, so I opted for the additional strength of a screw post at the butt instead of a lanyard tube. However, if you are a lanyard fan, there is still enough room between the blade edge and the screw post to wrap a thin lanyard around the post with a cow hitch. That keeps the lanyard centered in the handle instead of wrapping around it and makes for a sleeker package. Think of a typical flashlight lanyard where the loop that attaches to the light is thin and strong and the rest of it is 550 cord sized. If you must use 550 cord for the whole lanyard, pull the guts out of it so it wraps flat around the screw post.
I hope this helps you better understand why the Yo2 is the way it is. A lot of thought went into it and it is truly a reflection of more than 35 years of experience, training, and daily carry of personal defense knives.
P.S. As far as meat cutting tests go, yes, that was a big part of my personal R&D of the prototypes. Simple answer: It has more blade length than the original Yojimbo. It therefore cuts even deeper.
I hope this helps.