These rates have always been a pain in the proverbial and they have always seeems unfair, IME!
Some years ago I was based in the north and posted back to my old job, to a base in the south at very short notice, due to a shortage of instructors with my qualifications. There was a long waiting list for MQs and the schools couldn't offer a place to one of my kids, so I was obliged to keep my family in our own house up north (no MQs at my previous base either, we had bought locally - it was either that or a surplus MQ in the opposite direction from my previous posting for 2 years plus). I therefore commuted on a weekly basis, a distance of about 150 miles each way. I went to claim MMA but was told I was not entitled to claim any motor mileage at all as it was about 5 miles short of the required distance, according to the distance calculated by admin. This was about ten miles less than I actually drove; according to my car mileometer. As usual, there was no appeal!
However, I took a mate, who had been put in a similar situation to myself, with me. I drove him the extra 15 miles each way to and from his home. He was entitled to claim allowances as a passenger; I got nothing.
It was little perks like this that made me decide that was to be my last posting. Despite being offered Spec Aircrew, I took my option and walked.