@Avery4 It might be so much more simple. It might be putting fuel in the cylinder as you do it. Some people don't know how to do a compression test.
Some people pull the fuel pump fuse.. easier way is depress accelerator pedal (throttle) to WOT which *should* disable fuel injection during that time, apparently some models this doesnt happen.. but you may be seeing "wet" compression test numbers (akin to a small amount of oil in the cylinder) making your numbers go higher. This is how you can get about 230psi on a compression test.. wet. Dry maybe 140-ish.. should be different every engine.
Your battery may be protesting at the end of the last cylinder. You can turn the engine with the key 5-7 times before you stop. I'd let it turn over 7 times. Some let it go 5. Engine sounds different cranking with no plugs and firing.
This isn't a Ford with "Fuel pressure relative to manifold vacuum".. you're checking the ability of that can (cylinder) to seal during that 4-cycle turning. Suck Squeeze Bang Blow..
You also want to do it cold, if possible. Most accurate reading.
First thing I think when I see higher numbers are wet tests or warm/hot engine.. and to do it again, with the proper method, cold, before speculating about carbon on the tops of pistons (which you can see if you shine a flashlight down a spark plug well, at least on engines with the plugs right there at the top, maybe an inspection camera for engine bays with them crammed all up in there.)
Yep! 5 to 7 revolutions.