ether way I'd like the lore to explain more of how it works, I love sci-fi pseudo science.
The best theory I've heard is that MLF is based on mass AND electronic interference, despite the name implying that mass is the only factor involved.
When you look at the sensor size of the ships with the same hull mass and different MLFs, the ship(s) with the larger sensors typically have a higher MLF than the ones with smaller sensors. I'm not sure exactly how MLF would be calculated, but I suspect that it would involve scaling exponentials with sensor size and hull mass. Looking at the list of MLFs and comparing it to these values, It seems like box volume might be a factor as well with ships that are too big or small getting penalties to MLF.
That said, this doesn't really explain that much, and there are a few rather large outliers no matter how you try to handle the data. It's probably best not to look into it if you're expecting some kind of in-universe explanation.