Setting pre-exposure in partial frame sums

I would like to sum frames 2-10 out of a stack of 40. First I used Unblur to align all 40 frames and generate a shifts.txt file. Then I used Sum_movie to sum frames 2-10. My question is, after I specify starting frame as #2 and the dose rate, what should I put as the pre-exposure: 2.2 e/A2 which accounts for the 1st frame, or 0 if the program already knows we start from frame 2?

The pre-exposure here should be 0. Basically the pre-exposure always refers to the amount of exposure prior to the first frame, and it doesn't matter which frame you start summing from.