I've been doing a series of calculations concerning the possible fuel tank volumes of a TOS Rom BOP, the kinds of fusion fuels she might use and their implications, both as a warp vessel and as a straight-up, unmodified fusion rocket. The most interesting implications of these calculations is that a rocket's range increases as the percentage of fuel mass is increased, but that of warp ship increases as the mass of the fuel.
This is to say that a large and small rocket using the same fuel with the same efficiencies can have exactly the same ranges if they have the same percentage of mass dedicated as fuel.
A warpship, however, seems to be limited by the total amount of fuel it carries. Thus smaller ships using the same fuel at the same efficiencies can not hope to have the same range as a large ship, though she may have the same max speed.
Of course, our knowledge concerning the equations of warp power usage is basically nil.