yes and no, lets say you have a gasket leaking on the side where there is no water, you can say yes you will lose some compression becuase air can leak out as the piston comes down, but in all reality, you have 250 cc of piston coming down at roughly 1000-4000 feet per second depending on rpm, fluid dynamics say that the air is going to go to the least resistance. you have atmospheric pressure on the outside of your engine, when the exhaust port opening and the piston going down you have a vacumme in the chamber, according to physics the amount of air leaking out will be very small, so small that i have a hard time seeing a drop in running compression, BUT with no exuast heat you have no vacumme out the exhaust only from piston drop creating a low pressure in the cylinder, is a small hair line leak enough to change compression? still think you would need a pretty good chunk of gasket missing to show up on a compression guage.
that is also why a tiny leak in the crank seal or base gasket can make a sled run very rich very quickly, that same atmosphere pressure on the outside and vacumme inside the engine make the air want to get into the cylinder.
chances are if you are low on compression there is a tired cylinder from high miles or damage to the piston, rings or cylinder from lean burn or dirt.