MP changes result in about a 3.5% change in Mass air flow per inch of
MP and the mixture may not follow closely, depending on the engine. 
That means that the effects of 1" MP and 100 rpm changes are not the
same.  The change of 100 rpms has about 70% of the change of 1" MP.

Walter,

 

Thanks for the detailed explanation of the enrichment feature.  Apparently that works even though the mixture has been leaned?

 

At some opportunity I will do a further testing where I reduce both throttle and RPM another increment.  I guess the difference between 3 and 4 knots is 75% - I will try to remember to switch the GPS to Kilometers for greater accuracy (assuming I can stay in the same air mass).  To repeat, my point was for a gross diagnostic flight test of the MAP sensor. I think I used the word similar power, not "same."