It isn't necessary to live with large air pressure losses with the stock rear shocks. Just as is the case with tires, over time you will see some loss, but if you're losing more than a pound or two a week they can be fixed. First thing to look at is the plastic air lines where they attach to the fittings for the fill valve and where they enter the shocks. If the plastic lines aren't prepped correctly before assembly, they will leak. Test them the same way you would a natural gas connection, with soapy water and look for bubbles. If they leak, remove the line from the fitting and use a brand new, extremely sharp straight edge razor blade to trim the end off so it is square and smooth. Reinstall and move on to the next line until they all have been corrected. Next, check to make sure the fill valve core is tightened properly in the fill valve and isn't leaking. You can find a cheap tool to tighten them, along with a supply of replacement cores, at any auto parts store near the valve stem caps. Then, after making certain there are no leaks in the lines and fill valve, document how much air you are losing over how much time and then contact your dealer and/or the MoCo for shock replacement under warranty. No matter what they may try to tell you, it is not normal or commercially acceptable for an air shock to require constant monitoring and replenishment of the air.
You really need the specialized pump and gauge for these shocks, either from H-D or folks like Progressive Suspension. The shocks work with a small volume of air, and the pump & gauge need to have a special chuck that will not leak as you screw it on and off if you are to get a repeatable reading. And the official pump and gauge reads up to 60 psi, which is more than sufficient for the 50 psi max specification of the short shocks.
I still see what I believe are people comparing apples to oranges with regard to air pressure in this thread. The recommended air pressures will be significantly higher on bikes with lowered shocks. You may not know if you have lowered shocks, since the documentation from Harley kind of sucks on some of their bikes, but before you believe the guys with a CUSE who swear they run 15 psi with no problems and drop your pressure to match on a RK or RG, make certain what length shocks you have.
Jerry
BTW, I'm still looking for a 12 inch aftermarket air shock which would be better than the Harley Profile junk. Progressive and others have 13" models, but so far no one I've checked has a shorter version. Not interested in the adjustable on the fly stuff, just want the same seat height as stock but with decent damping and manual air fill.