The problem I have now, is that this means there is no longer a simple table to work from... you HAVE to do maths on the fly to work out how much fuel is used.
This is why I was suggesting that each ship have a standard number of fuel cells (e.g.: 50), so that fuel use per ship can be measured in cells. That makes it easier during most sessions, because you can account for fuel use like hit points or something. That way the complexity is reserved when they have to fill up the ship, calculating the cost of filling each cell at each Silhouette.
If the fuel cost has a range of 10-20cr @ Sil1 (average 15), then squaring results in cost of filling from empty:
Cost * Sil^2 (HWK-290) = 15 * (3^2) = 135cr * 50 cells = 6750cr
Cost * Sil^2 (Space Master) = 15 * (5^2) = 375cr * 50 cells =18750cr
You can get quite a few jumps and have several combat sessions before you need to tank up. Just judging from my own campaign, but this is close to in line what I've been charging. It also makes hijacking a fuel tanker pretty lucrative