For capital loss carryover, what is the correct income amount to put in on the AMT screen when AMT wasn't used in the previous year?

I have a capital loss carry over from 2017. After entering the carry over amount, TT auto populated the AMT income field based on nothing I could see. The help suggests if you didn't have AMT then you could use 1040 line 43... that value is not the same as the amount TT auto populated for AMT.