temperature at which contact quality improved exactly to the extent necessary to compensate for the (remaining) contact deficiency

This is perhaps slightly less wordy than the version I was thinking of a few minutes ago: " ... showed the precise level of improvement needed ..."

Alternatives to "compensate for" would be "overcome", "offset".

This is based on the assumption that one cancels out the other, i.e. that the improvement cancels out the incompleteness/deficiency of contact.

In fact I'm very tempted to go a bit further with the paraphrasing, and say "at which the improvement in contact quality precisely offset the (remaining) contact deficiency".

I've tried to think of versions that would match the Russian настолько, насколько more closely, but I don't think any of them get the idea across clearly (the idea as I understand it!).