Fret leveling questions

Hi everyone! I'm trying to wrap my head around this problem. I was doing some fret on a throwaway neck and found a couple of uneven frets in the middle of the neck. (I made sure to seat them down before levelling too!) While levelling, I came across an issue where the first few frets and the last few frets were being sanded down before the middle frets. I did make sure the neck was straight with a notched straight edge and the StewMac neck relief gauge. I was using a long levelling beam for the entire process, going back and forth and side to side. In the end, the frets did not buzz or cause any bending issues but it wasn't fully levelled when I looking at it with a straight edge. I'm worried that i may be shaving off too much fret material at the first and last few frets.

I have the StewMac fret kisser but I had the impression that it is only used for one or two frets. I also just picked up a shorter levelling beam to maybe tackle this situation. I will truly appreciate anyone who can explain to me this situation I'm having!

Thank you for reading!