Hi
I am not able to open X-Feeder triggers (but I can view the xml in notepad) so this should point you in the right direction.
In the trigger file there is a trigger called: increasing back amount by 1 unit
That trigger has a condition which has a formula value: starting_back*10
I think if you change the 10 to the value you want and save the trigger file it should work.
Needless to say please test your adjustment carefully in test mode.