I tried 3 different Fmods when I was crossing over my WH\harfedale evo2-40's...
First 80-12db, which sounded good but seamed like they were still getting more bass than I wanted and it was noticeable at higher levels, so I went to 100hz and it sounded better, my subs are crossed at 85hz... I then tried 120 since 100 sounded better than 80 , but it was too much and after having them in there for a couple days I noticed certain songs seemed to sound different than I remembered, so I put the 100's back in and went back and forth a few times, the 100's were the right choice...
So If you cross your subs at 80-85 try 100, if you cross your sub lower try 80...