today I only ended up using 5 gallons exactly

there are 2 differences between this batch and the last 2 they are

#1 an extra pound of DME and about a pound of extra steeping grains compared to the last 2 recipes

#2 I did a 3 gallon boil instead of 2

did the extra pound of DME actually fill up that much extra volume or

did my gas stove just not get hot enough to have a vigorous enough boil to get the same rate of evaporation as I got before

I am confused

BTW the final gravity was right on brew calculus predicted O.G. of 1.070 it ended up being 1.074