Yep, You guys got it.
Many use Kydex because it is very cut proof. All the nylon web sheaths we use for our fixed blades have kydex inserts that are screwed on at the pointy end.
This is so the edge of the blade will not cut the nylon fabric.
Kydex forms nicely to the shape of the blade even if Mr. Ken Brock always has to do things his way.
Ken, I've found I have good fit up until putting the sheath together with the final rivets then it sometimes gets too tight. This is why I use tape.
I use Cleco fasteners to test fit up my sheaths before final assembly. The Clecos are a temporary spring loaded fastener used in the sheet metal and aircraft building trades to position stuff until it is final fitted.
Another thing to consider when forming Kydex is that thin Kydex will cool much faster than thick Kydex. This means we have less time to handle the thin stuff when trying to position everything in the forming press.