Other way around. If you set it as large, there is no crossover as, then, all the center channel bass remains with the center channel speaker. Set it as small.

I have absolutely no experience with Klipsch centers but I would consider which option has the lowest frequency crossover between the horn and the cone drivers.

azfar wrote:

Their 2 way centers have 1500hz xover and 2.5 way has 500hz/1500hz. So the 2.5 way will make a noticable difference?

I doubt it. It is the crossover to the treble drive (horn) that is critical here and that remains at 1500Hz for both models. Now, that might be a better speaker for other reasons but I cannot say.

It is unfortunate that some companies do not offer real 3way center speakers.