Thanks to both Herring's and Charles' [Cr from Texas], I have had to refresh my memory and thinking on this subject... and actually had to do some homework.

Yes, a new vacuum pump can generate well over 20" of Hg. vacuum... keeping in mind that when we say "vacuum" we are really talking about any absolute pressure that is less than atmospheric... which is typically ~30" at sea level. IF you read the MBZ manual section on these pumps, you will see that the Germans devised a way for you to quantify both level and the strength of the vacuum being generated by the pump. If anyone is interested in reading such, I can send you the PDF file!

As to what is the proper level at idle, the MBZ manual does not really address this... but I now think this is going to be basically a function of several things:
(a) just how new and/or effective your vacuum pump still is,
(b) how many leaks you have in any of the systems using this pump as a vacuum source, and
(c) the adjustment and condition of the vacuum control valve [VCV].

So how do you know what the proper vacuum should be at idle being supplied to your "Auto Tranny-Shifter Control System"... before you apply throttle. Well my current belief is that you want this to be the maximum vacuum reading that still allows you to reach zero at full throttle while driving down the road in fourth gear. IF you are NOT able to get it down to zero, then you need to either:
(1) make the restriction smaller or
(2) adjust the VCV so that it bleeds off more vacuum... AND
in most cases it's a lot easier to use the orifices.
Or you can do as "yellit" did... install the smallest brass icemaker control valve he could find in this line to allow him to effectively adjust the amount of restriction. I still want to try this so I can more easily experiment more on this subject, but I want something less than the 1/4 inch ice-maker plumbing valves... and I want one that uses a metal-on-metal "needle" type valve rather than the typical rubber-tipped valves that press against a valve seat!

Then I will be able to more easily test my hypothisis [sp? <--- professor Charles]... first with a long, large diameter, vacuum supply line run from and back to the engine compartment with the restriction-valve in it. I say "large diameter" for you see a long line that was too small would itself introduce friction losses and thus effectively become a part of the restriction but would be lost when you removed it from hanging out the window!

I hope these thoughts are of interest to you herring... and to others who read this THREAD!
Regards,