Lee FCD for 10 mm

In .32-20, the FCD is open topped and it's easy to see how it works. The .40/10mm version OTOH has an adjusting screw covering the top and an internal sleeve. It's not clear to me what's going on inside it. As far as I could tell at a glance the sleeve does not have a top/bottom orientation, but maybe I missed it.

Last night I assembled some 10mm, seating without crimping. I was used what seemed to me to be a minimal flare (not really visible except maybe using the caliper jaws as straight edges along the sides of the case). By eye, the rim of the case is flush to the side of the bullet. How do you judge how much crimp to apply with the FCD?

I just measured the rim of three cartridges, got .4205, .421, .4205 I may have give the seating die a tiny turn past first contact with the case, but my untrained eye can't see any real evidence of a crimp.

I took the barrel out last night and did a plunk test on one round (probably not one of those I just measured). It went in like an otter and rotated freely.

I guess I don't need to run them through the FCD?

How does the handgun Lee FCD work?

I have two FCDs. One for .32-20 and one for .40/10mm. Lee's website is not, IMHO, terribly clear in explaining how they work.

The .32-20, which I guess is the rifle type, is easy to understand: the four fingers of the die clamp down on the case while the whole assembly pistons up, so there is no friction on the case, if I have that right.

The .40/10mm version is completely different. Is the internal sleeve just a taper crimper by another name? How does this differ from the crimper in the bullet seating die (which I've used in my first box of ammo screwed out past where any crimping occurs.)