Soundstage Heresy IV and Forte IV

I am interested in understanding the difference in soundstage between Heresy IV and Forte IV and the reasons for the difference.

Bass I can get, but concerning soundstage, what is causing the difference?

I hear that Forte soundstage is better than Heresy, but I also hear that the Cornwall soundstage is better than Forte. Arent Cornwall and Heresy using the same mid and tweeter components? Then why would Forte have better soundstage than Heresy?