IMO, the best way to handle this is to make the stuns less powerful outside and more powerful inside. Also instead of fading to a black screen, it should be white. It would also be cool to have a shake effect for a few seconds longer than the stun effect is. Course, I'm just aiming for realism here.
I dont think theres a way to make more or less powerfull insite/outside, texture can be changed, but that shake thing wil require some uscript

and stop playing BF.
-
the only thing that changed directly in flash was the effect duration, no other variable was changed.
the blackscreen disappear within 10~ seconds but the annoying sound stay ~25 seconds after the flash explosion. (with effect duration of 20, the sound stays for arounds 35 seconds!)