Flyback Diode Placement
In general, you want the flyback diode as physically close to the inductor it is catching the current from as possible.  Long leads mean inductance, which slows how fast the current can build up in the diode, which makes large voltages at the solenoid.

If the only thing that is at the end of the long wire is the solenoid with the diode and driving circuitry at the other, then the diode will still protect the driving circuitry well enough.  However, the possibly high voltage transients at the solenoid end of the wire can cause radio interference, and in extreme cases arcing.

With long wire to the solenoid, I'd want two diodes.  One at the solenoid to limit voltages on the wire, and another close to the driving circuit to protect it.  The inductance in the long wire can cause kickback too.