Ok trying to answer all the questions...
CPU is i7 7700K, not overclocked
Thermal paste is fine, I wiped off the stock and used Arctic Silver. Used a bit too much initially, which I discovered yesterday and rectified.
Radiator physically does not fit in any other position, the motherboard components are in the way when I try to put it at the top or on the back
Whoever said my cooler is upside down - you're absolutely right, however apart from being triggering to look at it isn't a physical issue, the cooling mount is an absolutely bitch to put on so I'm not going through that again for no change in temp/performance haha. I did it twice and wanted to kill myself both times. I don't think the tubes are stressed or too tight so for now I will leave it this way, but when I'm due to change the thermal paste again I'll switch it up then.