Boil Vol Basis

I have set up some profiles for BIAB methods.  What I am somewhat confused about is the selection of Boil Vol Basis in the mash profile. 

I have estimated that if I want 5+ gallon of wort into the fermenter I need approximately 6.5 gallon of wort at the start of the boil and it will be reduced accordingly during the boil process.

Thus I have set Boil Vol Basis to 6.5 gallon. 

Am I thinking about this properly??

Your thinking is correct.  it is just a place holder to give the user some idea of volumes when looking at the profile.  This number is updated by the software in the recipe when it is applied.

You will probably leave some beer behind in the fermenter (trub loss) so if you want to package exactly five gallons you should start with a little more going into the fermenter. How much to add will be dependent on your processes.

As "Oginme" says "Boil Vol Basis", and the other settings described as "basis", is only a place holder. It could be used for troubleshooting a profile before it is in use.

I came across these "basis" settings when noticing there wasn't something quite right about the profile's predictions. The predictions were missing the "deadspaces". Of course they were, the mash profile knows nothing about the equipment profiles! Until the profiles are combined in a recipe that is, then it all makes sense.