Motivated in part by the conclusions below, improved estimated mode matching efficiency from a poor 13% at the beginning of day to 48% (estimated using the reflection signal levels from the rfpd). What helped was walking the beam with the last two mirrors, and then scanning the cavity output coupler around to center the resonant mode which at this point seems optimal. This process was tedious, but effective apparently.

The distance between the two mirrors is ~ 45 mm which slightly undershoots the planned 47.5 mm which could limit the achievable 100% in simulation-land, but I'm moving on for now, hoping the lock will bump it up enough for the OPO threshold to be within our pump power range.