B757s within 4 nm often slow down a lot more than the following B738 etc. and I've often wondered whether the catch-up causes as many of the wake turbulence reports as the wing. In recent years many B757s have been retrofitted with winglets but I've never seen any research as to whether these have any benefit in wake turbulence reduction. As there are ever fewer B757s flying around I won't lose much sleep over it.
UK MATS Part 1 can be found
www.caa.co.uk/cap493 Appendix B gives our current 6 category groupings although it has been updated by
SI 2020/04 and further tweaked by some MATS 2s