One other observation:
If the STBY INV logic works the same way on the 146 as described in the Avro FCOM (which I would assume it does, given the shared electrical architecture), then the STBY INV switch should control a relay that switches the EMERG AC busbars between ESS AC and the STBY INV output.
With the switch at OFF, the STBY INV should not be powered, but the EMERG AC busbars should be disconnected from ESS AC and connected to the (unpowered) inverter outputs instead. This should result in EMERG AC being unpowered, and the EMERG AC OFF annunciator should illuminate.
In the sim, switching STBY INV to OFF does not produce an EMERG AC OFF annunciator. It appears that EMERG AC continues to be fed directly from ESS AC regardless of the STBY INV switch position. The inverter itself seems to work correctly (selecting STBY INV on the AC meter shows voltage at O/RIDE and no voltage at OFF), but the changeover relay that should switch EMERG AC between ESS AC and the inverter output does not seem to be implemented.
This would also explain why selecting O/RIDE with ESS AC powered does not cause the heading bug on the left HSI to wander, as described in the manual. I imagine that particular effect would be quite complex to implement in a sim anyway, so that is entirely understandable.
Related to this: when the STBY GEN is running (O/RIDE with engine 3 providing green hydraulic pressure), the batteries are correctly disconnected from EMERG DC and BATT 1/2 OFF LINE illuminate, which is great. However, according to the Avro FCOM, selecting STBY INV to O/RIDE while the STBY GEN is delivering power should reconnect the batteries to EMERG DC and open the ESS/EMERG ACO. In the sim, the batteries remain disconnected. This is likely related to the missing STBY INV relay implementation.
Of course, if the 146 differs from the Avro in this regard, please disregard!