Inequalities increase the distance; thus it by no means follows that the distance from A to B is equal to the distance from B to A--it may be fifty per cent.

or one hundred per cent.

longer.
The explanation is simple.

Distance is estimated by time, and, speaking roughly, ten li (3-1/3 miles) is the unit of distance equivalent to an hour's journey.

"Sixty li still to go" means six hours' journey before you; it may be uphill all the way.