it actually doesn't matter, some amps have sensitive potentiometers and some dont. More than half or half way doesnt matter if its matched properly with the head unit-preout voltage especially if its a weak pre-out voltage. Its not anywhere near clipping or distortion in that case. Just usually when the gain is over 70% to get full power, that just means things from the signal line needs to be beefed up. Not totally necessary but its nice to do. Either way your amp is still putting out the same power.