Leela ratio is arbitrary.
Also you can keep the Leela ratio the same and still have a situation that's favourable to SF (relative to old situation).
FastGM runs SF on 16 Xeon E5-2670v3 cores.
An i9-9900K is twice as fast per core.
LazySMP is lossy, both in terms on NPS gains per core and NPS overall. (So 10 cores doing 1 mnps is weaker than 1 core doing 1 mnps)
Giving SF 8 much stronger threads (instead of 16 weaker) would tighten ELO margins by a bit.
In the end it doesn't matter because you can only test with the hardware you have at hand.
But Leela ratio is dumb and can be gamed.