For me, I vary the hallyway heights. Optimun is relative as you don't want to cookie cut your maps with the same sized areas over and over (Might be more forgivable on a CTF or 5 point CP map).
For me it is just as important to pay attention to the width of the hallway as well. Take 2Fort for example- the widths and heights from hallway to hallway change (sewers, to main hallway, to narrow long hallway, spiral corridor, to main stairs leading to intel, Intel main hallways, to narrower hallways leading directly to intel room, ect)