I didnt know what I would think of the spey blade but now that I have it in hand I believe its a winner. The part i like the best is how low in the frame the blade rides when its closed.
I agree that the way a Spey blade sits deep in the handle pocket is very attractive for ease of carry of a slim profile when closed.
I made a construction paper insert for the handle pocket, and after studying how Clip, Spear, and Sheepfoot Charlow blade shapes interact with it, here are some observations.
1. If you press down on at the blade of a closed Charlow, you will discover that it will easily fit an additional 1/4" into the pocket, with 1/16" to spare, before bottoming out on the spring or head pin. But be very careful, as you can ding the tip of a sheep foot, or the edge of other blade shapes.
2. The sheep foot blade will hit the head pin at the very tip of the blade, before it hits the spring hump at the middle pin, but it is still possible to lower the tip of a Sheepfoot by 1/4" below the liners, without it bottoming out anywhere.
3. Because of the upward curve of the blade edge at the point, on other blade profiles, including spear, spey, and clip, there will be no contact with the head pin, only at the spring hump.
4. It appears to be a cutlery convention that the tip of a blade be set only about 1/16" below the liners. this appears to be an aesthetic decision, relating to the look of the blade spine in relation to the curve of the head of the handle.
5. The spear blade will be limited as to how deep it can sit in the pocket, because the pull gets so close to the liners that it becomes hidden. This is not true of Clip or Sheepfoot blades. The spey blade needs no adjustments of any kind, as it already sits as low as possible in the pocket, while still revealing the nail nick.
6. Filing the kick will lower a blade in the pocket, but it will also lower the back spring when closed, so it is not flush. Don't file your kick unless you're OK with that. I don't think cutlers will ever agree to build a sheep foot, or any other blade profile, with the tip of the blade as deep in the pocket as it will fit without touching, so the only way to get a deep set sheep foot, is to file your own kick, at your own risk.
7. Over time with sharpening, the tip of any blade profile can end up above the liners. The primary way to bring the tip of the blade back down below the edge of the liners, is to file the kick, so you end up with a sunken back spring when closed. This has no effect on the spring position when the blade is fully open.
8. Another way to bring a proud point back below the liners is to reshape the spine of the blade downward, which shortens the blade, but this approach does not produce a sunken backspring. I find this approach works well with Clip point blades that sit proud, instead of filing the kick, but it also works with other blade profiles.
9. When I lowered the sheep foot blade on my 2 blade Charlow, I also had to lower the kick on the pen blade, to keep the primary blade pull uncovered. Lowering the kick on a pen blade is challenging, due to the shape of the tang placing the contact point of the kick almost flush with the frame.
This pic shows a lowered sheepfoot on the left, and the stock position on the right
this is the effect on the backspring, dropped kick in front, stock in back
here is an unmodified spear on the left, and the drop kicked sheepfoot on the right
Here is the unmodified spear, in front of the dropkicked sheep behind, note the spines are essentially at the same height now.
Here is my 2 blade sheepfoot on the left, before modification, next to a single blade, also unmodified
here is my 2 blade sheepfoot on the left, after dropping the kick on both blades, so you can see the pulls, on the right is the dropkicked single sheepfoot
here is the resulting sunken backsprings on the modified 2 blade sheepfoot
one last warning, dont modify your knife if you dont plan to keep it, as it will detract from its resale value. Otoh, I am much happier with my drop kicked sheep, as the proud blade was very disturbing to me, especially on a single blade. ymmv