From: Winnipeg, MB
The Gorn understands the question. I did not ask if I got any combat bonus, I asked if my losses would be
lower if I had level 6 forts rather than level 3 forts. Since no one seems to know, I will withdraw the question.
Unequivocally, my experience is that you leave the forts to attack, so your fort level does not affect the combat calculations. If it did you would get a Forts + in the combat report.
That said, the Japanese always attack first in a given hex, so if both sides program an attack in a Japanese hex with forts and the Japanese attack does not retreat the Allies, I am not sure if the Japanese get to retreat back behind their forts before the Allied attack.
No matter how bad a situation is, you can always make it worse. - Chris Hadfield : An Astronaut's Guide To Life On Earth