Folks, there was already a great thread on this topic a couple of years ago titled:
"Mag Check in Flight"
It discusses power reduction, the reasons for doing so, altitude, etc. Do a search on this site and you'll find it.
I personally don't know jack about technical issues, but that thread seemed to make sense and seemed to have some sound reasoning for everyone's position.
and in the old days . . . we then held hands around a camp fire and sang Cum Bya M'Lord.
IMHUO
Keven
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E60