That is a fairly large card in a relatively small chassis, but it should have decent airflow with that case.
Is the card overclocked? You could just set a lower power limit to reduce temperatures. You won't lose all that much performance either.
Idle average will be determined by the zero fan mode threshold, you should expect it to sit high when idle.
Make sure all your fans are correctly configured. Typical would be front fans as intake, rear and top as exhaust.
I think pictures are needed here. Just a description and general parts list isn't going to tell us all that much. Also going to need a complete parts list, including CPU and CPU cooler especially.
idk how to put a picture here...
yes I use 2 front 120 mm noctua fan static pressure as intake
2 top deepcool static pressure too as exhaust
2 fan 1 noctua fan 120 mm
NFF12IPPC-3000 PWM
and one more is from master liquid 120 mm rear AIO mastercool
the top and front using same controller system fan 1
the rear and pump using same controller plug in to CPU fan
the case layout is the same as the picture default case with HDD bay below
I'm using mother board b350 gaming pro
CPU RYZEN 1600
DDR4 16 GB