Upping the storage limits can do that; the ships will then be able to maintain maximum warp for three turns, or fly at a slower speed for longer. Note that because ships generate their own fuel, they will always be able to travel indefinitely at slower speeds. It's the same thing as taking a quick run and pausing, or taking the trip slow and steady. If you remove all fuel-generating ship technology from the game, then it would be possible to enforce a radius of operations on ships.
Here is a balanced scenario, that would make the short runs at max warp an interesting design choice, as well as a strategy: Have the core generate supplies which, when added to two scoops produce a sustainable cruise speed listed under CruiseWarp:
Code:
TL MaxWarp MaxUse Core Scoop C+2S CruiseWarp
I 2 200 50 25 100 1.0
II 3 300 100 25 150 1.5
III 4 400 130 35 200 2.0
IV 5 500 150 45 240 2.4
V 6 600 200 50 300 3.0
VI 6 600 220 50 320 3.2
VII 8 800 260 70 400 4.0
VIII 8 800 260 70 400 4.0
IX 10 1000 340 80 500 5.0
X 10 1000 340 80 500 5.0
XI 11 1100 360 90 540 5.4
XII 12 1200 400 100 600 6.0
XIII 13 1300 500 100 700 7.0
If you allow a player to add as many ram scoops/bussard collectors/replicators to their ship as they want, players can get ships with sustainable max warp...for a price. It takes eight scoops of the appropriate tech, plus the warp core, to support max warp. If scoop tech is set to 10kT, then the result is the player has some interesting choices.
The figures above are balanced so that if the player adds two scoops, they will receive enough supplies to maintain cruising speeds listed (or stop to refuel between rabbit-runs at max warp.) If the player chooses to spend their hull space on additional scoop/replicator/collector tech, then they can usefully add up to eight of them to contribute towards a higher sustainable speed. Adding more will gather supplies towards fuelling weaponry between fights. But of course all those fuel generators cost space, so the result is less room for weaponry...
On another note, warp-9 and warp-7 are speeds that don't exist in the current core/nacelle configuration.