You obviously need to know stem length. Top tube length will also play a factor. Also important to consider saddle setback, hence which is why it is important to be able to try the bikes in person and make adjustments to saddle height, tilt, angle, setback, handlebar angle/position etc. as needed before comparing.
generally speaking, you can compensate for less or more frame reach by changing stem length accordingly, that is assuming that frame stack is roughly the same.
You can always manipulate the "effective" frame stack/reach with different stem lengths.
Don't forgot handlebar rise , reach, drop degrees whatever depending on flat/drop bar.