if you want since its in a protected area you can install the soffit first, space panel properly then when you measure the beam for the wrap add a 1-1/4'' bend at the proper angle to cover the soffit edge,you can eliminate the j channel this way.Depending on the soffit profile you may have to install a 2x2 piece of bent aluminum where the beam and ply ceiling meet first,more complicated but what most pro's will do