Inductance of a three-phase transmission line
A transmission line of this type can be modelled as a single pair of wires carrying current to a load and, at any one moment in time, there is a forward current on one wire and a return current on the other wire. Given that both wires are partially magnetically coupled, the magnetic fields produced cancel at the mid point between the two.

Now, if the wires are some greater distance apart, there is still cancellation at the midpoint but, each individual wire has more “spatial freedom” to generate its own localized magnetic field. The result is that there is more flux per amp produced and, this translates into more inductance.

It’s not the flux linkages that create more inductance (because forward and return currents are always opposing); it’s the self inductance of each wire that increases as the distance increases.