SG of fuel and fuel distribution

[A.FLOOR]

The aircraft i fly (airbus) has a fuel distribution chart corresponding to a sg of 0.785

Now obviously when the sg is higher, the litres of fuel required to make up the weight of fuel is less.
We give our fuel order in tonnes.

So if we order 20T @ sg 0.785, we get about 25480L
And if we order 20T @ sg 0.805 we get about 24800L

Hence a difference of about 700L

How would a higher sg affect the fuel distribution?

thanks in advance