It's sounds counterintuitive but sometimes playing higher can blend a bit better , I've noticed that alot of 60/70s bass players would play higher than people do now , don't know if rubbish amps had a part in it but sometimes the bass being closer in pitch to the guitar can thicken it up a bit , Noel Redding , Andy Fraser , Entwistle etc , if there is a riff in G for instance try it at fret 10 on the A string