The Oregon 511AX is a pretty good grinder. But they are not perfect. A ‘semi-precision’ device.
A few options:
Install a ‘perfect’ (new?) chain in the grinder, with the power ’OFF’; adjust the grinder head to match the chain; and record the Right and Left index plate readings. Use those settings (e.g., the settings 23° Right and 27° Left might give you the perfect 25° cutters R and L).
As above, but use some type of machinists’ tool / gauge to measure the 25° on the grinder, or off finished chains.
Instead of using the ‘offset settings’, above, remove the metal index plate, enlarge the mounting holes, and shift / reinstall the plate correctly (I put double-stick tape on the back to help hold it in place).
Philbert