OK, perhaps I've figured out what's happening (although i'm not sure how to fix it)
My yard is pretty big, so the matrix is small in comparison..when I apply an effect directly to the matrix, it renders fine at the proper resolution, but when I apply an effect to "whole house" which includes everything, it renders very blocky..I'm thinking due to how small it is on the "whole house" group model.
Does this make sense?
Attached are the model previews of my matrix...one with the pinwheel effect applied to the "whole house", and the other with the exact same pinwheel effect applied directly to the matrix....notice the difference in resolution of the diagonal lines. The direct matrix effect is pretty much pixel level accurate, but the whole house one is using a much lower resolution.