Star Trek

Why on NX-01 has horizontal warp reactor and on U.S.S. "defiant" and "voyager" has vertical warp reactor.

And on NCC-1701-E has vertical warp core:

I not know why on early starships warp core has horizontal form. Maybe somebody can help me with this question.

I don't think whether the warp core is horizontal or vertical affects its funcitonality. I think it has to do with the design of the ship. They have to find a place to fit it where it can be ejected quickly in an emergency.

The warp core is really just a chamber where deuterium and anti-deuterium are mixed, so I doubt the position really matters all that much.