If I'm using rockets to get to Mars (or back) and I know that there's a point of closest approach to Earth based on each planet's orbit, what's the difference in fuel used going to be between that close-approach transit and the 'farthest distance' transit? Are we talking about 10%, 30%, 50% of fuel? I know there are other factors that will apply, but assuming one wants to make the transit (it might really, one supposes, be two answers - closest approach vs. furthest approach with each different origin (Earth or Mars)?

I don't need hard numbers, but I'm curious what sort of order of magnitude might be involved? I know it has to use more fuel and/or time to make the longer transit vs. the shorter, but I have literally no concept of even a rough % of difference in this respect.

I imagine it isn't just a ratio of separation distances because of ballistics and how we'd accelerate with a rocket, etc.  And giving a lot of the trip might be coasting, the difference might be almost all time and very little fuel (or a lot more fuel to hit higher speeds so the time is not a lot more).

For simplicity, I'd imagine you'd want to consider an instant impulse vs. the real situation of 'ship gets lighter as fuel burns, thus thrust produces more delta V'.

I guess aligned with this would be a related question:

What are the most likely lengths of time for Earth to Mars / Mars to Earth for a) fuel/mass economy and b) shortest time Earth to Mars given typical engines we might have access to? I ask just to get a ball park idea of how long it will usually take a crew to get to Mars and how fast one could get there if it was urgent given the limits of limited fuel/mass?

TomB