Attacking the monsters in front of the portal is NOT selfish. It allows you to hit spinners as soon as they spawn out of the portal, and sometimes even reach spinners that other players can't get to, particularly if there are brawlers in the way. And you're not going to find a spot 1/10th as good as it for chinchompas. Just direct people - when 3 or 4 monsters pile up, tell everyone you've got spinners and they should hit the portal. Far and away the best thing to do is run right to the rightmost portal, and stand 2 squares back from the middle square in front of the portal. Wait for 3 monsters to spawn - every single monster that comes out of that portal heads toward the void knight in a straight line, so you'll block them all right in front of the portal in one big stack. Once there are 3 monsters there, start hucking your chompas. You'll distract any spinners and they won't heal the portal, and you'll get massive amounts of XP - not 1k per toss, that's an exaggeration, but you'll easily get 300-400 per toss. And even on the best worlds, enough monsters will come out of the portal to be worth it.