Homergah
Only I didn't say fudge
I don't know if this has been covered, but.... It's certainly not the vigor of your boil causing efficiency problems. If you are boiling too much your gravity would be HIGHER than expected. You're not boiling off sugar, which means you are concentrating it. I have found the absolute best way to know where you are at and where you are going to be, is to use gravity units, not just gravity. 4.25 gallons of wort @ 1.060 is not the same as 5.5 gallons of wort @ 1.060. 4.25 x 60=255 units. 5.5 x 60=330 units. Read Designing Great Beers for detailed explanation.