My advice would be not to underestimate the size of the site. Even for those of us much younger than 70 the walking can be intense. So maybe try to pick out just a few things they really want to see and try to stay at one stage for a few acts rather than go Pyramid-Other-Pyramid etc a lot, as it’s a lot further than you think (esp when crowded).
I say different markets but I don't think anyone can really. Sam can been given an extreme bump up for the case of the other headliners theh have. Could have subbed easily but it is what it is. Even if you give him the benefit of selling the venue you did out twice it's 17-18k tickets and you're then registering around the sub level point. That's assumption.