The level in the bottle itself makes absolutely no difference, as such.
What's important is that coolant level is higher than the leak. By that I mean, if the coolant bottle was on the floor, it would fill completely. Therefor the air would rise to the highest point within the engine somewhere. That then becomes the level, u bends and air locks aside, if you see what I mean?
Provided the coolant is above the leak, the leak will show when pressureused. If its not it will just blow air out instead.
And btw, pressurising the coolant bottle isn't the only way. Depends what you have to hand, but it can be pressurised by breaking into the system at any point. For instance the coolant pipes to throttle body are very handy, if you have a foot pump with a football valve adapter for instance, the diameter happens to fit the throttle body pipes. Just block the other end obviously.
But given the year of your car, I'd look for core plug leak on the back of bank 2 cylinder head first off. Between dis and head. Awkward one.