Thanks Robert.
I started playing with advertising intervals and surprise surprise that’s where the power goes.
The documentation mention “between connect events”. I interpreted it “while advertising” but that’s apparently not the case. When the radio is not transmitting, I measure 4uA which is great. Also because the Radio is still on and a peer can connect almost immediately.
Another trade off I considered is to manually time advertising using an external RTC and put the MCU to deep sleep. But doesn’t seem a great tradeoff.