I have gone from BTE to RIC and vice versa. Personally with my loss I have needed to go with the Naidas, which are more powerful.
I don’t think there is any advantage in speech in noise with a RIC. I think for severe losses it could be worse. I trialled a RIC recently and it was awful in noise, but I’m unsure if that was because it was a bad fit.
I would check your prescriptive formula on your Phonak Lumitys. I assume it’s the Lumity Naida SP. If it’s the Phonak Adaptive Digital it might be worth asking the audiologist to change it to NAL-NL2. It made a big difference in noise for me.
If that is unsuccessful it might be worth trialling the Intent or BTE power that is now available from Resound.