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.