Help Sizing a Sheath

I really want to buy a David's Sheath, but I've never had a wereable before and don't know what size to get. Do they expand somewhat? Because I know my own measurements, and none of the three sizes approaches my actual circumference. The smallest size is also too short to fully cover me, and the medium would be just a bit too long. Can anyone with experience with wereables help me out?

 

I have the David and the Crackers sheaths and enjoy using them both. I am cut and average size. I have the small crackers and the medium David. Based of my experience a little longer is better than shorter. Hope this helps.

 

Just got a medium myself, the other day. Like OP, my girth is a bit more than the toy is internally. I'm 6" long, 5.5 circ. With a little lube it slides right on, stretches A-OK and feels comfortable. Only problem I've noticed is it has a habit of sliding up on it's own, usually about an inch and a half to two, and I'm thinking this might not be as much a problem if I'd gotten the large size. Hope this helps somewhat. Feel free to ask if you've got any other questions ^^

 

Hiya, I'm kind of a newbie to bad-dragon stuff so forgive me if this sounds stupid but...
What is it like trying to use a sheath too small in length?