I confirmed with a test that NRF_POWER_MODE_LOWPWR is the default once in the setup loop, so no need to explicitly enabled this. When I turned on constant latency mode the idle loop power increased to 377uA.
I also found that the DC/DC converter is NOT enabled by default. This does not impact the idle mode power, however, this does impact the advertising and connection power. I didn’t test this directly, but the online power profiler linked above shows significant savings with the DC/DC converter enabled.
Looks like the proper call to enable the DC/DC converter with the soft device is: sd_power_dcdc_mode_set(NRF_POWER_DCDC_ENABLE);