Answer: That's a good question (something I can mumble while fishing for an answer).

I think a general rule would be that, large note or small, the accidental counts if it is indicated within the staff, as opposed to within an ornament sign. Gardner Read offers this example in which the eighth note C is resharped even though a sharp C was already indicated in the ornament:

A more ambiguous example might be a turn like this one:

Since the C is sharped within the staff it's more evident that it is still sharped when it appears as a quarter note. But if that turn were written as follows a sharp would be required on the C:

For a real-world example, here's something from a Clementi Sonata:

Clearly that accented F must be sharped; it can survive without carrying its own accidental.