AM is a bit of climb but very useful once you are comfortable. You are making good progress. I still think you are confusing the terms. You need to get a firm grasp on the difference in zenith and azimuth or we are talking past each other. like this
the OEM head shell does have zenith adjustment,
you can adjust zenith on almost all headshells, if they have slotted holes, you can rotate the cartridge and adjust zenith. rotate it looking down from the top. Many do not have azimuth adjustments, rotate it looking at it from the front.
you should be able to get these closer 25.42 db (r) 23.12 db by adjusting azimuth. Round off your readings as you look at them.. 23.1 and 23.12 are not significantly different
I think the .45% and .48% IMD you reported earlier is suspiciously low, perhaps impossible. While 5-6% is much higher, it is not horrible and more realistic. I suspect you can change the Zenith to lower them further then try VTA.
changing the Zenith, turning the cartridge ever so slightly, I mean teeny, tiny amounts where you aren’t even sure you moved it, can make a huge difference. It is just something you have to keep doing until you get a feel for it. Screws a bit too loose and it moves too much and won’t stay, a bit tighter and you can’t move it.
I’m talking about turning (twisting) it looking straight down from above rotating it clockwise and anti-clockwise.. again, so little you aren’t even sure it moved, a fraction of a degree.
then you have to check Azimuth and overhang and VTF and VTA again, and so forth. Unless you slid the cartridge back and forth while adjusting zenith then overhang won’t change but check, VTA and VTF likewise, but check them.