The Nebula and Miranda are lighter vessels than the Constitution and Galaxy.
Whilst they have similar components, they don't have the same power output. The Nebula was meant to be smaller (R.Steinbach), but forgot that they needed to scale the windows and bridge module as well as the ship.
Anyway the nebula has smaller impulse engines (weird, considering the galaxy suffered complaints of them being too small), reduced fire-arcs, sub-optimal nacelle placement, and reduced hull space for deuterium storage, so a shorter operational range.
The miranda is simply smaller than the constitution, even though it has similar weapons, it wasn't given the same warp core. It's a smaller ship in a different capability range.