849 prep fill area cleanup

@doutriaux1 @aashish24 

Had an hour to kill and took a stab at optimizing the vcs scalar bar implementation. Ended up cutting the time down from 0.262s to 0.89s on my machine.
This replaces the `a.append(a[-1])` line, since it seems to me that if these don't match, it's a bug. I can change this back if it is needed, though it isn't causing any test failures this way.

If we revert it, make sure not to revert the bug I fixed in the first patch of this branch.