with the holes you have in the very back I would say making the other holes bigger would be a bad idea. You may want to contact the manufacturer, and find a way to beef up the top so you can open your top up more.
on another note, moving your light forward, and angled to the back may work with 90 degree optics. I'm not an expert just what I would try.
I think no optics close to water would limit penetration.