nRF9160DK LTE Sensor Gateway low power operation without UART?

I'm using the LTE Sensor Gateway sample (NCS 1.7) to transfer data from a BLE sensor to the nRF9160DK up to NRF Cloud. To get low power operation, I've been able to use the PSM feature to reduce LTE radio power draw, but my current consumption floor is still around 900 uA. I believe this is due to the UART being on.

When I try to disable the UART through proj.conf and spm.conf (as referenced in this blog post:, I get a compile error. I imagine it's because this project needs the UART to communicate with the onboard nRF52840, via the HCI LP UART project that is programmed on it.

My question is the following: given the need to have UART enabled to talk to the onboard nRF52840, is there any way of reducing the overall current consumption floor? In my application, I'm ok with putting the nRF52840 to deep sleep until I need to use it, but I wasn't sure how best to do this in the LTE Sensor Gateway project. Any help you can give would be much appreciated, thank you.