hop efficiency issues

my last ipa i clocked around 80 ibus on beersmith and it tasted more like 50. i decided to bump it up on this next batch to 100 and this tastes just like the one before (50ish). i do AG on stovetop, so i dont get a heavy rolling boil...but it still boils. i also use hop bags. im probably answering my own question...as im going to start using a propane burner and stop using hop bags. i was wondering though how many of you have had hop efficiency issues when using hop bags? or could there be another reason why im not getting a legit hop bitterness/flavor?

Are you boiling the full volume? Less than full leads to reduced utilization of the hops. Also the bags may be restricting the "agitation" of the the hops.

6.5 gallon boil down to 5 at about 90min.