At first, I thought I had two options, but really the notch at the rear is the only feasible option as the wire will stay in this position without the caps. The front notch would require the caps to hold it in place, making it more difficult to adjust and putting sideways force on the plastic caps. You can spin the caps to fit 3mm or 2.5mm cable.

While adjusting the cables, I found it quite easy to just lay the mast on the grass, and while sitting, push against the mast with my feet holding onto the wire. And just leave the caps off while making the adjustments.