Hello: How much can one read into a float charge of 13.3 vice 13.6?
Well, I almost agree with BT, I'd say "nothing significant" rather than just nothing. In general, a lower float charge would indicate that your battery is weaker to begin with, or there are wiring losses higher than there should be, or the charging system isn't putting out as high a charge as it might/should be.
If the battery is load tested (or at least, tested with the float burned off and after allowing 24 hours for the chemistry to equalize internally) and the charging system is tested in operation, and both test out OK, then whatever the float charge measures, is normal for your setup.
13.3 versus 13.6 could just reflect the different between two meters. Rule of thumb, unless you have a recently calibrated high quality meter, is that the rightmost digit may be off by 2-3 numbers from meter to meter, and that's just because cheap meters aren't intended for high precision.