I think that between the high TWR allowing the vehicle to spend less time in the thicker parts of the atmosphere and the lower pressure 'wake' the ship on on to

I think that between the high TWR allowing the vehicle to spend less time in the thicker parts of the atmosphere and the lower pressure 'wake' the ship on on top would produce, there isn't as much drag over the fins as one might think. IIRC it was one of their various "delightfully counter-intuitive" discoveries during earlier testing.