Just an idea. Aside from tradition, is there
any reason no to put one wide box pleat
in the under apron? It seems like it would
make modesty a little easier, particularly
in the more puritan parts of the USA.

In my case, where my waist size isn't
exactly stable, it would be easier to
accommodate the expanding width
with minimal re-stitching.

It would also help balance the weight,
if only a little, on a rear-heavy tank.