Here’s one of their product manuals that may not be the same model but the terminology should cross over. If you search the doc for “RTK ratio” there are only 2 mentions and neither one of them did anything for me but you might make some sense of it.

This results from the ratio test performed on the potential “Fix” solution. It shows how many times is the best solution better than the next one. If this number is more than 3, Reach will consider RTK solution Fixed.

So, all values higher than 3 can be considered ideal.

The AR Ratio formula is the ratio of the sum of the squared residuals of the second-best-fixed solution to the sum of the squared residuals of the best-fixed solution.