thank you for your response!
First - you are correct. I checked the reading sensor for the 28c and it was assigned to a CPU value but this value never changed and remained static at 28c - maybe this is actually the mobo as you suggest. I pointed this to the "CPU Package" and this instantly started to reflect roughly the same value as the cores (around 70+C).
I have now checked the factory fan settings and even at 70c the fans are only set to 45% so, as you say, maybe this is perfectly normal. Just seems a bit freaky that the CPU will peak out at 100 so to run between 65 and 80 all the time is a bit of a head challenge!
I've got a support email in with AORUS to see what they say.
Again, thanks for your help!