Those kind of changes can be expected depending on the tube. The Russian (Sovtek) rectifiers run a bit hotter than some of the others. It is still pretty well within spec for the tubes used.
Personally, I wouldn’t make changes to the biasing there. Biasing hotter (more voltage) gives you more headroom and more power, thus more volume (theoretically). But the tubes die quicker. Running these as you are describing is not really running “hot” as much as a but hotter than with the other rectifier so you are really in a good place with your measured levels.
Tube curves are a fun thing to get into. Here are a couple good sources:
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