Your second expression is what's called a "cascading expression." Each time it's evaluated, After Effects must evaluate the expression on the layer above it, which requires After Effects to evaluate the expression on the layer above that, etc. This isn't a big deal with a few layers, but as you get more and more layers in the system, it can get pretty slow to render.
The first expression is significantly faster to calculate, because each one can be evaluated independently. I can help you adjust your expression if you like, but I'm afraid I don't quite understand what you're after here.