RB compression

[TunaCanTuner]

I've been researching RB swaps for awhile now, but can someone explain to me what causes the RB25DET to have higher compression than the RB26DETT? I've always read the bottom end of the RB26' was just a stroked RB25'. Is the difference in the head?

[misnomer]

I have no exact figures, but likely the RB25 has a smaller combustion chamber (above the stroke of the piston). I'm not sure how the bore and stroke compare between the two motors.