Re MG's point about temporary starvation due to the oi-feed line being empty on the engine side of the tap, I (being paranoid) always open the taps on my AMC twins (Trev is so right about them, they're quite notorious) a bit ahead of myself, to be sure of a loaded feed pump before starting. Been doing that for years, plus rigged up a mag earth (in the style of the taps available from Dove and others mentioned ages ago in the linked thread). Although draining is attractive, it's a bit of a palaver as well as messy depending on what bungs are where - and it means washing rural waste products off the underbellies.
Funnily enough, my A seems to behave well if left at tdc per LJ's comment, but isn't a bad offender even at its worst to be fair. Seem to recall there may be other reasons NOT to leave engines deliberately at tdc though, although I can't think what they are now and I've never had any trouble.
My worst wet-sumper is without doubt a Norton Atlas engine, which I am resigned to draining after leaving standing for any length of time. Massive spanner needed for that, too.
My best is my alternator B31, which never ever lets a single drop drip down, and has yet to use any oil at all, nary a single tiny drop, between 1000 mile changes. Stunning, probably a measure of luck involved (piston from Draganfly, a nice rebore and new valves and guides about 10k miles ago) - and my favourite all-time bike even if it is slow. (I know . . . I need a B33 and/or to get out more).