Proteins in the meat tighten (e.g., think of handmade hamburger patties on the grill). I like to thrown down bits of the sausage to make 100% coverage that way, the same way I do with the sliced cheese.
Did you roll it out between wax paper? If not, try that.
I'm pretty much applying it like they do in that video I linked to - the little bits at a time, like you mentioned.
RCB, I think you may be on to something about moisture control. I may be over-draining my tomatoes. Next time I make an sausage patty deep dish, I'm going to use the Muir Glenn Crushed w/basil straight out of the can and see if that makes a difference.
Garvey, I might just have to use smaller bits when I put the sausage down. Early on, I tried rolling out the sausage patty into a disc, but it wasn't very practical as I kept tearing the wax paper while rolling, which would get stuck in the sausage.
DD, there were a few occasions where I've made my own bulk italian sausage from lean ground pork, and yes, I think the shrinkage was minimal, so a leaner sausage would be good if I could find one (or make my own again).
Pythonic, I WAS IN THE POOL!