Well, as these are X-ships I'd imagine the megaphaser has seen improvements as well. Such improvements like higher output, higher efficiency, and like other technologies, a reduction of the size of the components. Take computer hardware. An extreme example: today's pocket calculator has more computing power than the room-sized UNIVAC of the 1950s.
So how about reducing the size of the megaphaser emitters, making them less prominent on the rollbar? Or instead of a cone like on the first Reliant, how about a precursor to the phaser strip of the Next Generation era ships? Like a small raised dome or oval with a 360 degree range?
Just some ideas for you to ponder...