Offhand, I don't remember.

MAYBE it is a difference for "At Risk" losses (Form 6198) versus Basis losses (which do NOT use Form 6198).  Although that isn't what I remember, my memory isn't super clear on this point.

Are you using 6198 for that calculation?  If so, *IF* there is a different between calculating At Risk loss versus Basis loss, that is the problem.  Form 6198 is not used for Basis losses.  You would need to manually do it.