>I feel Emma was less indulgent, beneficent and condescending to the Coles than Mr. Weston and Mr. Knightly.

Coleses would compare Mr Knightley’s and Mr Weston’s behavior with Mr Woodhouse.
I think there are as many chances of interacting with Mr Woodhouse as there are with Emma if one accepts the circumstances mentioned by you, according to your quote that follows. After all Emma too isn’t out so much (and especially not at Miss Bates').

>IMO Emma is acquainted and has exchanged civilities with them when it could not be escaped—perhaps after church, just in town or at the Bates apartment:

Dinner parties were out but visiting may not be. We see him visiting Randalls. He has been down vicarage lane
“But I do not like the corner into Vicarage-lane.”
This could be to church, and his politeness when meeting the Coleses there should be enough encouragement. Emma would be as polite as she is even to Mrs Elton.

Emma has shown herself to be polite when thrown together with people she doesn’t like. Mrs Elton’s company is also irksome, and Emma finds her vulgar and illbred.
If one has to *draw parallels* then based on this if she met Mrs Coles at Miss Bates’ (which is very very rare) then I think her behavior was gracious. Even with Miss Bates she isn’t rude. The Box Hill event was the first time.
Mr Woodhouse not dining out means Emma doesn't either, and that's no encouragement for any host/hostess to be inviting.

Highburians don’t need to know people much in order to form opinion. We see Mr Knightley doing that with Frank Churchill and Harriet. Emma with Robert Martin (though she has a strong motivation there), so forming opinion about the Coxes isn’t any different.

>“it would be much better if they would come in one afternoon next summer, and take their tea with us” (25) which I cannot imagine he would suggest if they were strangers.

I think the idea of inviting them to tea has come from having to refuse their invitation. Both the invitations, one real (from the Coles’) and the other proposed (by Mr Woodhouse) are a ‘first’.

>Emma’s reflections on her performance at the Cole’s party are hilarious and I think do her no credit.