I do not see how shape of Bullet would effect Pressure behind or against the rear of the Bullet in interior Ballistics, other than, as you mention ants, that a Boat Tail ( or a Round Ball ) may allow a little more early gas to blow by, and, a flat base would not be imagined to do so as much...upsetting being left aside.
I doubt very many people shoot Boat Tails in Pistols, unless an old Remington XP or some other relatively exotic ones, chambering what are Rifle Cartridges, anyway.
The stories of the early WALKERS 'blowing up', because of people loading Conicals upside-down, did not make any sense to be.
Round Balls have about as much Aerodynamics, as the Cone of a Conical, if they were imaging the Gass to be deflected against the Bore because of the shape? makes no sense, regardless.
The pressure of the expanding Gasses behind the Bullet, will not be any different because of what the shape of Bullet, or the rear of the Bullet is...the shape, whatever it is, gets pushed against the same as if it were merely a cross section of the Bore...however many parts of a sqaure inch that is as a bore section, is what is being pushed against by the PSI of the Gasses.