Too large a drop when you begin spraying is a sign of either a poor regulator, a regulator running at too high a flow rate for its design, or running the compressor at too high a flow rate for its capacity.  A couple of psi is okay, but too large a drop may indicate problems.  With a single action brush you can lower the flow rate a bit which may help.

I notice some folks really open the airbrush up, and use it like a spray gun. It is not a spray gun.  Consider it more as a brush that puts down paint without making brush marks.  

M1, you keep asking away!  It's so true when they say the only dumb question is an unasked question.  And don't feel bad about wondering about the PSI.  Want to hear something funny?  I've been using an airbrush and compressor for the past 16 years or so and it wasn't until last year when I discovered the whole "pressure drops when I depress the trigger" phenomenon as well.  It took the good folks here on the FSM chat forum to explain things to me.

Whenever I'm getting my airbrush set up to paint something, I get the tank good and filled, then I depress the trigger on my (empty) air brush, then while holding down the trigger, I set my air brush pressure.  After that, I'm pretty well set to go.

Eric

You read the pressure while you are pressing the trigger on your gun. The psi drops as it flows across the nozzle. The larger the airbrush nozzle, the more the psi drop. So set your psi while you are pressing the trigger on the airbrush.

You are airbrushing at the lower pressure, the one that is sustained as you paint after you depress the trigger.

That difference in pressure is why people say to start off the model somewhere,,,,,,that big puff of air at the beginning can blast quite a bit of paint that you aren't ready for.

Rex