good guesses PK.
and i'm not expert as well ,
and would defer to Eric Gorr for a full and accurate explanaition.
my take though?
150 is "ok" but a bit low..
but honestly typical compression testing is so "subjective" that few OEMS even bother to give numbers anymore.
one guys 150 is anothers 175 or 128,, not enough consistency in the testing method itself, ,(not the individuals,bu tthat variers greatly too?)
the eyebrows ,, do make it slightly easier to kick/ or start.
they do not effect the engines running compression..they are far to low in the cylinder for that as they ar esiomply reliefs in the upper part above the exhaust ports
as for your 04 500AF
whens the last time tghe top end ewas fresh? the run time , a physica linspection of the bore to piston ring clearence,
and wether it sucked up any sand is a better test than compression testing it...
AJ