beer calculator question

This may be a stupid question but here it goes. I am doing a full boil recipe that calls for 7 gallons at the start of the boil and down to 5.5 at the end. I am cutting it close with my pot. It has about 2 inches left in the pot when at full 7 gallons so I was thinking of going down to 6.5 at the start. I should have 5 gallons at the end of the 60 minute boil right or will starting with less than 7 gallons boil more?

Do you think the 2 inches I have left at the top of the pot would work? As long as you control the boil at first you should be good as the wort evaporates.

Also, I have always done extracts where I have mixed 2 gallons of wort with 3 gallons of cold water. Doing a full boil without mixing, is there anything different I need to do different?

I would be a little nervous with 2" of head space in the pot as it may overflow. I guess you could try it but watch the pot like a hawk. I would decrease the boil to 6.5 gallons and then top off in the primary to get 5 gallons. I don't think that 1/2 gallon of top-off will really make that much of a difference. You may want to re-calc your recipe with a 6.5 gallon boil to make sure your hop utilization is in the same ballpark.

I'd start with 6.5. If you're brewing in your kitchen you'll likely have a hard time getting a vigorous enough boil going to boil off 1.5 gallons in 60 minutes.

I use 210k 30 psi burners and in 60 minutes I typically boil off 1-1.25 gallons.

Why not start with 6.5gal, boil off 0.5gal, add 0.5gal of boiling water and continue to boil to the 5.5gal mark?
H