Not just poking, but I find that when drawing objects from a sheath is is so much easier to draw them from a canted position.. especially when sitting or driving.
I am sure we can think of a way to have a reliable bottom retaining device. Perhaps somehow capture a smaller diameter O ring in there so you have a speedbump but have less chance of it firing an unlocked P+.
If you don't mind aesthetics just making the bottom diameter sliggghtttlyyy smaller with a heat gun may work as long as it does not hit the button.
Examining the P+ some more David machined the body a slightly smaller diameter at the center. This may be key if you make your sheath have a slimmer midsection. Since you have a 'slit' the sheath can flex like a clamshell.
Heck.. if we are daring enough I think a slick way to make a clean retaining device would be to somehow use the venting holes on the P+ to 'click' in place by somehow deforming the kydex to fit in the holes.. but realistically the holes are too small.
Alas, this almost makes the exercise a job instead of a hobby : )
As far as the cosmetics, I held off mentioning that as I know some people take it personally when someone says "Your item might get scratched if you rely on a friction fit." What I did for mine was mold it without a friction fit and built up the inside by lining it with masking tape. Some custom makers use moleskin or whatever to line sheaths but that was too much work for this application. Plus I'm not that good : )
As far as the foam, I don't typically use foam when molding cylindrical objects or flat objects that don't necessarily need a "pancake" form fit such as knife blades. Tubular sheaths, 'bikini' and loop (such as the one I did in the pic) I just do freehand. However since you have a pancake design I see the benefit. When I do use foam I use some scrap plastic foam I salvaged from old monitor and computer boxes I got from my old job.
The "pros" use these..
Sheath Making Foam - (12x11.5x1) - (KYDEX™/Concealex)
It does seem expensive but I haven't graduated to a level where I have started shopping for alternatives.
Finally, I guess great minds think alike.. I was also thinking of forming a second bolt on sheath that holds 3 ml bottles like a bandolier. Thanks for the good thread - it influences me to continue the hobby on my side too.