Thanks guys for your replies.
What would be the maximum FSD boost jump with 32 tons of fuel?
The fact you have 32 tons of fuel is irrelevant to the question. * It doesn't matter how much fuel you have on board, you can only use 5 tons per jump.
5 tons of fuel will let you jump whatever the maximum distance is for your current build. If you're using a 50% boost, 5 tons of fuel will let you jump 150% of your currrent jump range.
So, how far can you jump on 6 tons of fuel? You can't make a single jump using 6 tons of fuel, each jump will use a maximum of 5 tons of fuel no matter how far the jump is.
Does that make sense? In short, if you're using a 100% jump boost, your jump range will be double what it is unboosted and that's regardless of whether your tank is full to the brim or only has one jump's worth of fuel in it. **
*OK it's not totally irrelevant (in theory) because 32 tons of fuel has a mass of 32 tons, so strictly speaking you should be able to jump further after using half the fuel in your tank because what's left only has a mass of 16 tons. In practice though, the galaxy map doesn't understand the concept of using fuel reducing mass and therefore increasing jump range - when it calculates a route, or works out whether you can make a jump it does so treating your range as if you have a full tank of fuel, even if you don't.
** If you're even remotely confused, don't bother reading this because it will probably just make things worse lol. There does seem to be some kind of rounding or error margin in the calculations for boosts. Yesterday I attempted to use 50% jumponium to make a jump. My Asp jumps 50.40 light years unboosted, so with 50% jumponium it should jump 75.6 LY. I tried to plot to a star which was 75.57 LY away and got the 'route plotting failed' message on the galmap.