That case is cozy and designed for up to 2x 120 mm front intakes and up to 3x 120 mm back and top exhausts, and it looks
like it has a problem feeding the GPU fan with the drive cage blocking airflow from the lower front intake and the airflow from the upper one goes mostly over the top of the card.
The marketing drivel of "[t]he smart design channels air directly to your graphics card to provide it with the cooling it needs for intense gaming" on that page is belied by the picture below where the GPU fan looks to be taking in air that's sitting above the PSU, the channeling from the lower fan drawn in looks sus to me.
So rather than going straight to adding fans, I'd probably first try putting your radiator as the bottom front intake and the 120 mm fan intake above it, if the hoses reach, hoping doing so might partially feed the GPU and hopefully cool it.
Then when that doesn't work I might try the rad as the back exhaust fan, taking the slight hit to CPU temps, and trial both 120 mm fans in the front intake positions, before adding any new fans in the other 2 possible exhaust positions at the top.
Obviously liquid-cooling your GPU would solve the problems the case gives you...