Your root error is that hoch (correct declension: "hohe") does NOT actually describe the adjective sozial (correct declension: "soziale") here - it does describe the entire noun phrase soziale Position, so it has to be congruent to the noun.
eine (hohe (soziale Position)) - "hoch" does get declined
The position, which is social, is high.
- Also grammatically correct, but not what you wanted to say:
eine ((hoch[ ]soziale) Position) - "hoch" does not get declined
The position is social, and the degree of this socialness is high.
In the latter case, "hoch-" will usually get appended to "sozial", but I guess you could separate them if you want. The standard case for adjective modifiers is to separate them:
eine ((ziemlich soziale) Position) - "ziemlich" does not get declined