The problem is many fuseholders are not exact, but fuses themselves even less so. I've seen many where the end contacts were not concentric with the glass bit, on crooked and the like. Combine that with a holder that is not made perfectly and its really easy to see how shifting the fuse around a bit to get a better fit can affect things. How I do it is to simply measure the voltage drop across the fuseholder, then rotate the fuse until I see the lowest drop. Easy enough for someone that isn't going to zap themselves (which you can do easily enough, so don't mess with the fuse if the circuit is live).I understand and agree with your findings. But, fuses like Padis and HiFi Tuning seem to be made to a higher standard. Padis has no info etched on the sides of the end caps to ensure uniform contact and are as even a possible, which I've confirmed by rolling them on a flat surface and they don't waver. The same goes for Hi Fi Tuning except for the markings on the end caps.
The fact that Mundorf worked with Hi Fi Tuning on their Supreme fuses (which I haven't tried as I love what the Silver Stars do) using their formula of 99% Silver and 1% Gold in the plating and the melt wire itself tells me there's more quality control going on with their fuses aside from others that seem to burn them in like a cable cooker would do to a cable and calling it Quantum Tunneling or something equally vexing.
All the best,
Nonoise