I'm _well_ below 3000ft AGL (if you check the SF chart, you'll see the
whole area I'm talking about resides beneath a 1500/3000 foot SFO
Bravo shelf).

Transponders only need to be calibrated to within 300 feet, so the
granularity isn't important, as I mentioned, I find it FAR easier to
hold a 250 or 750 altitude anyways because I can just reference a
horizontal line on the altimeter.

And, this is just my personal practice, I _do not_ vouch for it beyond
that, and If anyone has an issue with it, I'm interested to learn why.