Standard socket depth is 3/4" for 2" fittings, as it says at the beginning of the Charlotte catalog (page 12 on my version). 2" san-tee shows a vertical center-line to base of socket measurement of 2-5/16"; the p-trap diagram doesn't give a measurement from weir to base of socket, so it may be as low as 0" but I think it has to be positive, so I'm going to call it 3/16".
That means hub to hub p-trap to san-tee would give 4" from vent center-line to weir. If we assume the "two diameters" rule refers to nominal diameter and is measured from the edge of the interior of the vent, that would be 3" for hub to hub. So at least 1" of plastic pipe should be showing between the hubs for a 2" p-trap to 2" san-tee in plastic.
Cheers, Wayne