A roll is matched to the type of wire, not only to the diameter. A V groove works with solid steel wire, a knurled groove with flux cored wire that has a soft sheath, a U groove with aluminium and soft wires, because it does not bite into the surface. The same diameter in the wrong groove gives slipping or flattening.
Set the pressure by hand. Feed the wire out, stop it at the nozzle with a gloved hand and increase pressure until the rolls start to slip on the wire. If the wire is flattened or curls up before the rolls, the pressure is too high and you are causing the birdnesting yourself.
A two roll feeder is enough for 0.8 and 1.0 mm solid wire on a cable up to 3 metres. With aluminium, with 1.2 mm wire and above and with cables of 4 metres or more, choose a four roll unit, because it splits the drive force between two pairs and does not deform the wire.
Rolls are a wear part. The groove wears and loses its profile, and feeding starts to pulse, which you see as an uneven pool and hear as an uneven arc. Check the rolls at every liner change and replace the set rather than a single roll.