Beermith2 batch size vs Brewers friend discrepancy

So with the way I have my equipment setup which I've been using for about a year now I have a post boil volume of 6 gal then with cooling shrinkage and trub loss I have a batch size of 5.5 gal and a bottle volume of 5 gal. However there's a Brewers friend calculator that calculates your projected og based on your preboil volume and pre boil gravity and that states in order to reach my og I have to boil down to 5.5 gal not 6 gal as beersmith states and I've had to almost boil down to that much my last couple of batches. So idk if I need to adjust my equipment profile, never remember having this issue in my previous batches, don't know if it was the poorer conversion of using wheat or rye in my last couple beers or that I went to a thinner mash. I I just a curious as to why one program says x og at 6 gal while the other saysin order to reach that same fg I have to boil down to 5.5 gal.

 

While I have never used the Brewers Friend app I suspect the difference is due to your efficiency settings.
Also, if you need to adjust your gravity up or down you can do it without changing your boil time. Beersmith has an adjust gravity tool that will calculate how much water or dme to add to go up or down. That way you can hit your target OG without changing the boil time. Just take a preboil reading after you mix up the kettle well and make your adjustment.

 

Hmmmm. Didn't know this. Well now I can make up for any efficiency loss. Thanks.