First question is what shape aim point do you use? If you're worried about mm accuracy you need to be using a thin cross as an aim point mounted exactly to the vertical & horizontal with a sprit level,
that way you can set the reticle cross EXACTLY over the aim cross, which is the only way to know you have the exact same aim point for each shot.
Next thing I would do is check for crossover by shooting at 35-30-25-20-15yds, if the POI moves L/R then the scope is not central along & parallel to, the bore,
That would most likely be the mounts, especially if using the type fixed at one side with a loose clamp on the other side, use a set that split vertically & self-centre.
What baffles me with the element helix is they seem to claim 1 click is both 1/4moa and 1/10mrad which is simply not possible