More important to spray the top of the leaves since that's where the PM is, yeah PM usually does start on the bottoms, the RH swings are probably higher at the bottoms vs the tops, plus less light. You could probably just spray the bottoms daily or every other day if you wanted.
Spray all through flowering?? Yeah depends on the plant if I can spray all through flowering I guess. Meaning some plants have no lower buds and some do. I really don't want to spray the buds I guess.