To my amateur eye, there appears to be limited fuselage on the engines for Sukhoi fighters from Su-27 on. That is, the fuselage follows the curvature of the engines closely and there is a definite material difference between the adjacent fuselage.
This seems to be a characteristic specifically of Sukhoi fighters or their clones.
What is the purpose of such a feature?
I realise might be a state secret as to the actual design decision and will accept such an answer but I suspect there is a straight-forward engineering reason. And perhaps I am mistaken on my assessment.