I suggest you review post 22.
Even a Ransom Rest can't zero a pistol for your grip and hold.
I don't understand the reluctance to evaluate the gun at 25 yds.
After reviewing post 22,if you shoot to a horizontal line with the sight picture level/flush,you have established the 25 yd variance between POI and POA for elevation..
Till then,forget all about center hold versus 6 oclock hold. Shoot only at the horizontal line. Once you have that data,if you prefer a 6 ocklock hold with an 8 in bull at 25 yds,GREAT! Set t up 4 in high from a horizontal line . That MAY mean a taller NM sight or equiv. Till you get the elevation,don't confuse the issue with windage.
After you have the elevation,you just drift the rear sight,but focus on perfect sght alignment for windage.
I suggest using a measuring tool such as a calipers to make adjustments to a calculation rather than beat and hope.
I get it,you paid a lot of money. I've found the combination of paying lots of money and having reasonable expectations often leads to buyers remorse..
If they will work with you,work with them....to a point. If they truly are not delivering quality,go ahead and out them.You owe them no favors.
For myself,I know shop math and I can run a Brideport mill.I can make a sight.
Maybe that's not possible for you. Most sight manufacturers will ft a sight for you. Talk with them. It might be if you do as I suggested in #22,you can send them just the slide with instructions "Its 22 inches low and 14 inches left at 25 yds from where I want the POI"
Its just shop math. They can fix that.no problem.
Without implying anything...I'm not there,be careful to assess wheter ts the gun (they can fix) or the shooter (they can't fix,but you can)
25 yds. Elevation,then windage. Large sample size Collect the data. Machnists can work with data