if I remember right, the distribution of the warp field occupies the whole of the nacelle. you can't just tack impulse engines on the nacelle butts, they'd be tied together in power distribution. if the core went down, it'd take the impulse power with it. that's why the impulse deck it tacked onto the butt of the saucer. I'm also thinking of the protection of the impulse drive and fusion deck from hits. this
is a Scout class, after all.
i need to make a "whole" pic. the ship is actually just a saucer with two nacelles tacked on.
Ryles:check my sig. the Kings are a derivative from these intrepids, and have the next contract numbers up. they still have the Borg to worry about, now that voyager's shaken up the hornet's nest
in universe note: my character is an old hand retired admril from a VERY thinly popuated species that bolted from their homeplanet just in time. think Mackenzie Calhoun with a muzzle and a specialty in starframe design and modification (they've been buying leftovers and retirees off the Klingons and even the Romulans!)