Now I'm not a a boffin with these things as I do not fly gas turbines. But the EPR of two is always the same no matter what. The reason is that pressure measured at the PT2 probe would be 2 x PT1 probe so it would be the same for all engines. The thrust would be derived from the acceleration induced into the intake air stream which is accelerated by the combustion chamber. So the reason the -17 engine has more thrust is purely due to it working with more fuel burned in the combustion chamber.