Dear Langudo,
Sorry for the late reply.
Regarding the issue for not able to install Floe Riing 280 RGB in Level 20 RS ARGB Case on top, could you give us more details in current circumstances? Usually Level 20 RS ARGB could support 280mm AIO on the top and at the front.
To install Floe Riing 280 RGB AIO at the front, it is recommended to install the two 140mm radiator fans at the opposite side to provide push-pull effect airflow, and meanwhile you could reveal full RGB lighting of the AIO.
If you have any questions, please let us know. Thank you!