As a standard vs unknown villain i raise 3xBB 70% of hands from SB.

If im up against a villain that 3bets 18% of the time, coldcall 43% and folds 38% of the time.

What kind of adjustments should i make, should i raise more/less? Bigger or smaller raises?

Maybe there is some earlier thread about this topic i have missed.

I have to guess that HU has shifted towards a 2.5x open though it's been years since I specialized in HU because of sites decisions not to run them well. 6max has shifted towards smaller opens.

As to your question it's reallllly gonna depend on how they react to 4bs. If they overfold then you should mix in more 4b bluff hands, good candidates are suited aces that block his ace combos but have equity when called. If he hates folding to 3b then the obvious adjustment should be made, take him to value town. If he is well balanced then you just have to GTO it and mix in some bluffs, again usually suited wheel aces but done less often than to a guy that overfolds to 4bs.