the reason why you want it close is because the wires can add additional inductance which if it's high enough can cause emf and arcing.
Which happens to be complete nonsense! If by "close" you mean having the diode adjacent to the inductor.
Just for the record:
I find it surprising that even educated engineers can resort to "magical thinking" about the situation, with assertions about "current surges" and putting the diode as close as possible to the inductor because the inductor "generates" the surge.
That turns out to be an absurdity. What generates the transient is not the inductor but the switching device, either a mechanical contact or a semiconductor. The inductor - as a response - acts to maintain the instantaneous current flow by generating the "back-EMF". So you provide an alternative path for it to do so through the diode. It is still the case that the current through the inductor and its connecting wires does not change rapidly.
What does change rapidly is the current through the switching element and the power supply which suddenly drops to zero, and the current through the diode which as a consequence suddenly rises from zero to maintain that same current.
The significance of this is that if interference is going to be caused by electromagnetic radiation from a suddenly changing current, that suddenly changing current is located in the loop formed by the power supply (or the local bypass capacitor), the switching element and the diode but not the wiring between the diode and the inductor. The need is thus to minimise the length of that supply - switch - diode loop by placing the diode as close as possible to the switch and power supply (bypass). It is these three that must be close together. Suggesting you need to place the diode close to the inductor (or motor) is actually quite wrong!
On the other hand, there is a voltage transient caused by the switching which can capacitively radiate interference. This impulse is - again - caused not by the inductor but by the switching element so it actually radiates - possibly counter-intuitively - from the switching element to the inductor however to all intents and purposes, all points on the wire connecting switch, diode and inductor experience the same transient so this is not affected either way by the location of the diode.
So now let's take a look at that transmission line.
I won't consider resistance; the simple model of a transmission line is a series inductor and parallel capacitance. The capacitance can perhaps be considered at each end. Well, the transmission line inductance is in series with the primary inductor. If you put the diode at the switching device end, then the inductance acts with the primary inductance and as described, resists sudden changes in the current which is to say, minimises inductive transient radiation.
If you place the diode at the primary inductance end however, you have now created in the transmission line, a second inductor in series with the primary which will add to the voltage transient at the switching device and enhance inductive transient radiation. It may not in itself contain enough energy to damage the unprotected switching device.
Capacitance at either end of the transmission line will indeed serve to slow the voltage transient but will conversely cause a transient when the inductor is switched on. Capacitance toward the inductor end will tend to cause radiation from the transmission line while capacitance at the switching device end will increase more the current surge seen by the switching device.
Note the general principle that it is the transmission line which radiates interference due to switching transients and the current transients occur in that part of the transmission line which is on the switching device side of the diode, so placing that diode near the primary inductor causes all of the transmission line to be such a potential radiator while placing it at the switching device limits this to the loop originally described, formed by the power supply (or the local bypass capacitor), the switching element and the diode.