Stupid boil off not calculating correctly

Yesterday I brewed a one gallon batch of a black ale recipe I formulated loosely off of New Belgium's 1554. I'll hold off on posting the recipe until I decide it's something I want to admit to creating. I am getting frustrated by my inability to properly calculate boil off. It's humid in Texas and humidity lowers the amount of boil off that occurs. It seems no matter how much I reduce the boil volume going into the kettle I always end up with a sizeable amount more than I should. I end up having to boil down some of the wort to make it safely fit in the five liter fermenter without losing a lot of beer to blow off. The problem with boiling down is not only the added time to bring wort back to boil, boil, then cool, but also continuing to boil for 15-30 minutes means the flavor additions are getting pushed back.

I started off calculating one gallon per hour as most resources suggest is appropriate but that is not even close. I tried lowering it to 3/4 gallon per hour but that also seems like 1/3-1/2 gallon too much. Next time around I'll have to try calculating at 1/2 gallon per hour. The problem is that I use the stove top BIAB set up for these small batches but a turkey fryer for the large batches, so I have to be mindful in my recipes that I make adjustments for the right set up. However, even though I used the turkey fryer for the four gallon lambic batch in December it still seemed to fall far short of boiling off a gallon per hour even though it was a very dry day and the turkey fryer puts off a lot more heat.