Hi all, trying to work out an easy way to match up the soffit boards of an angled soffit with the gable overhang. 

We’re installing raised heel trusses with a 2’ overhang of the 2×6 top chord. 

Gable overhang will be framed with lookouts and a barge rafter. I’d like the soffit boards to be mitered at the corners, so I’m guessing the gable overhangs will need to be the same size as the eave overhangs so that each soffit board has a matching mitered board at the corners?
In other words, does the diagonal length of the eave overhang need to match the horizontal length of the gable overhang? I’m a bit confused on this detail. 
thanks,
Adam