I mean, if you were using soothing to chi gen, then you need to use it when someones at max health because...wait for it...you need the chi (lolrng). That being said, jab and expel harm are better and should be used for chi gen. I only use soothing to put on EnvM...but normally I tank heal with HS during progression. EnvM is just to help make tanks more stable.
I run heroic spirits of the sun/relic of chi ji because they give the most passive intellect and the highest spirit regen. (I don't like proc throughput, but proc spirit can [almost] always be useful).
I have those trinkets and 8800~ spirit passive (prepping my gear for next patch) and I don't think I've dropped below 50% mana on any fight, though this is speaking from our farm clears this week (so all of H HoF and H protectors). This entails me wasting mana I normally wouldn't because otherwise I'd mana cap, and thats just bad. So instead I waste mana and generate some more tea. Hard for me to give mana advice to others without seeing logs though.