HI,
Since the RTX3090Ti doesn´t have any components on the BAckside which are producing heat, like the RAM on the RTX3090, we won´t produce an active Backplate for the RTX3090TI Series. IF you have high memory temperature then is something else not correct, like the well known package Probleme. To check this you have to remove the water block and check if all thermal pads have a imprint. IF not your GPU is affected with the package problem and you can send us photos of the imprints to info@alphacool,com. Then we can check it and send thicker thermal pads to solve the problem.