Instead of that.
It may be enough to toggle the high precision tangent basis.
It’s in the build settings of the sphere mesh and it prevents the pixellation break downs which aren’t really due to the “mip” of the reflection, but to the normal values of the vertices used to mathematically deform the reflection.
Since OP is directly dealing with spheres, that’s probably the best solution.
Ps:
Considering the cr ap state .27 is in at the moment, I still don’t get why 4k reflection captures work fine for me 