I think we talk way too often about fish holding fry or aborting them. I find that fish which are well treated, which does not mean undisturbed but just not overly harassed or cooped up, will drop just as they should. If you use one of the tiny breeding traps on one of the larger livebearers, they will sometimes drop a day or two earlier than they should but the widespread talk of holding or aborting fry is just taking rare happenings and making them seem everyday things.
If you are selective about what fish you keep, a 2 foot tank is often big enough to retain the best 10 or more of your adult fish. That can be enough to see a quality improvement in just a few generations.