IF the tester has a 1-way (ie schrader) valve then there would be an offset to the reading equal to the cracking pressure of that valve. i think for most schrader springs that's in the <5psi range. in this application the lowest spring rate would be best.
if that valve is as close to the cylinder as possible (on the plug adapter?) then the ultimate hose length/volume wouldn't matter.. but you WOULD have to make sure you fully pressurized the hose by turning the engine over enough.
if that valve is instead at the gauge, and you have a long length (volume) hose, then your accuracy will suffer, as you are adding the volume of the hose to the combustion chamber.
if you don't have a valve, you don't have a choice... as short as possible is the only way.