"Bikini bottom" to me is a misnomer, because these provide more coverage than the typical bikini.  They're perfect when paired with a tankini top.  The "medium" fit as expected.  There's no risk of unintended bun exposure, but nothing on the leg to flop up when swimming, either.
I've become a big fan of the tankini, which looks like a one-piece but allows for bathroom breaks without having to totally disrobe.