I can think of 2 ways to reduce power when using digital modes. The first reduces power for all modes via RV1. That control can be adjusted to set the power for the rig. The other choice is to reduce the audio drive to the uBiTx from the PC software. This would allow full power when doing SSB, and reduced power when doing digital.
Digital does have a higher power level than the other modes, so reducing the audio drive would be a good thing. Monitor the temperature of the finals and adjust accordingly.