I wonder how big the yellow perch (from April/May) are now. If they were 4-6" then, I would think you might have some 8" ones by now.
YP of that size would be eating the fatheads right? But 100 of them for a 1.5 acre pond is not much especially because they would not have spawned yet.
The size of the existing YP perch population is an important factor in deciding how many SMB to stock if you can only get fingerling SMB, or even juvenile SMB.
The condition of the fathead population will also be an important factor for the SMB next spring.