"Ron Garret"
If you fly final with some amount of power (which I gather most people
do -- I always have) that seems to guarantee that if you lose your
engine on final you will land short, and there's pretty much nothing you
can do about it. Is that true?

Unless you do every landing power off with room to spare, yes. Or, aim for
the mid point of a 2500' plus field. There are ways to do it. But, almost
nobody does. Base turn should be doable power off in most cases in a 172 or
similar glider.

Or have I missed something? What
should you do if you lose your engine just after turning base to final?

Land short. That's why the slow idle check during the run-up is important.

moo