Oh I see. Now I am using X63 RGB for my 5800X and it has reading of 31-32C on Ryzen master for 5800X in ide. But I felt hard to switch to H150i Elite Capellix.
My PC case fits 360mm radiator at the front ONLY with tube sides up but allow top mounting for 280mm. This is another factor to concern because tube sides up is not a best orientation but it is doable if at least I kept the pump downward the tube side of the radiator. If H150i have better performance, I may try it.
One question for you've got 40C idle, did you mount it at the top?
Second question, did you use dust filters to cover the radiator. It affects performance as filter blocks the heat to release.