Have you found this thread from earlier this summer? It has lots of good info.
Your total goal COA of 20K will be hard to attain with merit aid alone unless you are willing to look at lower-ranked ‘regional’ LACs.
We are a full-pay ‘donut hole’ family who were on a LAC merit-hunt for for our D21, and I wrote up a summary in the thread linked below. I don’t know anything about how merit and need-based aid stack, though, so I’ll defer to other posters on that topic.
Good luck to you: it’s a lot of work to chase merit aid at LACs since they are very opaque about their pricing.