Jason,
for starters
just like any game call,duck call, tube call, There is a proper way to blow them. I have alot of guys come to my house that say they are use to blowing a crow call and stick the mouthpiece several inches into thier mouth while covering the end of the call, almost treating it like an owl hooter. totally killing the sound. and getting too much spit on the reeds, therefor making them stick.
Doesnt matter if it is plastic or wood or even treated wood, its going to stick eventually.
I tuck my lips up under my teeth and just barely touch the end of the reeds.
feel is personal preference, i round my sides off and flat on top of mouth piece. This is what feels good to me. I have used Buckners crow call for as long as I have known Mike, and his are more rounded as well...
Now comes the internal diameters. This is all crucial for total design and sound....and your mouthpiece design has to match up with this part or you can get a really sour sounding call. i have tried so many different variations and have boxes full of parts that didn't work out.
With my molded mouthpiece, im getting the same exact sound I wanted in my wood mouthpiece, without losing a thing. Im also able to sell them cheaper, and still give them a custom made look
hope this helps ya
Gregg