Register and ask your own question!
Based on behaviour observation it remains unclear how are members considered worthy. According to doc there's latency consideration present, but it's not clear if it's latency between driver and mongo router or latency between primary and secondary.
My issue is that when querying from region which has one local secondary present, but primary with other secondary is in remote region, query seems to end up randomly in both regions. If I remove last 'fallback' readPreferenceTags, which allows other regions too, then I get results with expected latency.