You are both kind of right! The valve will close when the pressure either size of the valve has equalized – i.e. if you are pumping up the shock (or a tyre, same principle) the pressure in the pump between the gauge and the valve will be the same as the vessel being pumped up so when you detach the pump a hissing noise will come out but its from the air in the pump not the vessel as the valve is already closed. You therefore do not need to pump up past the wanted pressure to account for loss in detachment.
However, if you reattach the pump to the tyre or shock to check the pressure, a small amount of air will escape into the pump as far as the gauge reducing the pressure in the vessel. Not an issue on a tyre but it can be with something small like a -ve shock chamber. Note; even when you reattach a pump the pressure indicated on the gauge will be correct, just a little lower than before you attached the pump to it.
Oh, and original question – about 15psi less than RS recommend although when new I used even less but as they have thoroughly broken in and become less "sticky" the amount of air needed to get the right sag has increased (on reba, pike & now revelation)