After carry out the exercises edited into my earlier post I have come to the conclusion that if low on Gas, level off, chop throttle and reduce RPM to min. When at 160 MPH, go to full throttle, increase RPM to keep speed at 160 (indicated). Do not climb - the benefit of altitude is not worth it because you burn too much fuel climbing (stay high if you are there already!). Interesting that I was on Full throttle in all three tests. On both lower RPM tests at high and low level the throttle was max, boost at 0 at the same indicated speed of 160 (True - 164 low lvl 220 high lvl)
OK I appreciate this is probably not the best setting, for the Spit 16, but I do know what to expect of it.
160 is a safe low speed for the aircraft and keeps drag low.
It all goes out the window if you have an engagement to worry about.