I generally iron the perimeter tight, then come back and heat gun or iron the center area tight, and last, I iron all the ribs for the very reason John stated, torsional strength. I do this very same thing on small trainer type wings or my giant scale wings, too me it is just a good way to go. Here is my wife holding the stab and wing half for my 55% Extra 260 and both are covered the way I explained. Do you think the aileron on this wing adds lift? LOL

Bob