Why the Additional Aircraft Fuel Tanks Add So Little?

[Fomka]

Maybe I misunderstand something, but extra fuel tank for X-COM Aircraft adds very little amount of fuel. Interceptors have 1000 units of fuel by design (look here), and the fuel tank adds 20 more (here). It is a tiny gain of 2%! Very little and 100% useless.

What if the tank can be attached to a mudranger, the craft with the minimal fuel capacity? The gain will be 20/140=1/7, not bad, almost useful.

Maybe the fuel tank addition must be 20%, not the flat 20 units?

[Solarius Scorch]

The bonus is expressed in total units. So yes, it makes sense on E-115 powered craft, bot not much on standard.

[Fomka]

Ah, the precious Elerium, so rare and so powerful! Thanks.