Always shrouded in the mist of mystery, when popular casting mechanics focuses on spey issues it seems to enter the realms of magic.
It doesn’t help that the various styles of spey casting seem to compete in presenting their respective approaches as if they were different techniques, instead of just adaptions to some particular conditions.
Fortunately spey is spey, and physics is physics, and the latter governs the phenomena involved in the art of throwing a line with a pole in exactly the same way, whatever the brand, length or taper of your rod and line, and the waters and fish you are after, be it in Scandinavia or in the Pacific North West.