ive seen several discussions on this site about rc insurance. here is an excerpt from one homeowers policy. exclusions. the ownership, maintenence, use, loading and unloading of aircraft. (this would be the aircraft exclusion) but reading on it gives the definition of aircraft.
An aircraft means any contrivance used or designed for flight, except model or hobby aircraft not used or designed to carry people or cargo. therefor rc plane would be covered for liability under this policy. as all policies are different you should check with your insurance agent.

You are correct. AmA insurance is secondary after your homeowners. (primary if you don't have homeowners)

But if you have AMA insurance you can fly at an AMA chartered field.

If you have AMA insurance and the club is an AMA field, then the landowner is covered.

Often the land owner is reluctant to allow model planes to fly on thier land. Offerring the land owner coverage can entice them to allow RC flight on thier property.