Greek - στ is very tight

Greek - στ (sigma tau) is very tight

It looks like this is because τ (tau) is itself spaced very tightly with zero on the left and 50 on the right like lowercase latin t. However the tau is optically more alanogous to Cyrillic te ( which is space 50 on both sides ) so I suggest taking an approach to the left side bearing which is looser or perhaps even a mirror value to the right side.

Similarly, it is important to be able to easily pick out or identify the right stem of sigma and I think it should also be looser.

image from Roboto flex wght 100