O.K. I've finally thought of a possibly substantial benefit of the t-foil over the inverted T-foil. Without a fuselage and stabilizer, a fin with a wing has to contend with moment force wanting to force the board nose down. I've found that with my T-foil, moving it either forward OR rearward leverages that force and makes it worse. In the vertical length of the fin, a wing at 55 cm down would have much more leverage on moment force than a wing at 15 cm down.....

That said, it's hard to compare my fin (even theoretically) with the Virus fin because my goal is to accept the extra drag and moment force in return for planing at low wind speed with smaller sails. The Virus goal is to sail faster than a regular fin by getting more of the board higher out of the water. In this regard, it is difficult to increase top end speed even with full on racing foils.