I am fitting a thermostatic shower valve into a stud wall.

The feed pipes will be surface mounted on the other side of this wall
(as they will be hidden at the back of a cupboard).

I got a couple of male 90° 22-15mm compression couplings to fit onto
the end of the pipes and up into the valve hot and cold inlets. This
way the pipes can go straight through the wall at a right angle.

When fitting the 90° couplings to the valve, how do I make them both
point in the correct direction (i.e. at right angles to the wall, so
they meet up with the feed pipes) when they are fully tightened?

When dry fitting to near maximum tightness, they end up pointing in
completely different directions, neither of which is 90° to the valve
body!

Do I cut then ends so that they point where they should when they
"ground out"?
If so, how do I calculate this?

Many thanks,
Deano.