"In 2019, I have 30K short term gains on 1256 contracts"
your info does not make sense. you can not have just $30K of stcg from 1256 contracts. gains and losses on 1256 contracts are split 60% long term 40% short term.
if you have net 1256 losses they must first be carried back to 3 years assuming you made the election for the loss year. you can choose how much to carryback
however, there is a limit. it's the smaller of your net 1256 losses less $3,000 (or the net capital loss shown on schedule D that can be carried over to the next year assuming no 1256 carryback election is made. (say $100K in net 1256 losses and $20K in other LTCG AMD $10K in other STCG. $3,000 in net capital losses is allowed. c/b is $67K
there are also limits to the amounts that can be used in the c/b year.
smaller of (these are before the 1256 c/b)
1) net 1256 gains for c/b year
2) line gain 16 of schedule D.
