Yep, you got it. The 75 gal steel tank used in he ETO was eventually almost totally replaced by the 108 gal paper composite tank, or the similar size/shape steel tank. Some units continued to use the 75 gal tank though.
The metal 'tear drop' tank used in the PTO and CBI theatres, although similar in shape to the 75 gal tank, was of larger capacity (as I mentioned, I can't remember the exact capacity), and of course a physically bigger tank. The suspension point, at the centre of balance of the tank, meant that the tank would therefore hang at a different angle, and, of course, it would protrude further forward than the smaller 75 gal tank, in order to clear the flaps.
Simple as that.