I would guess the publisher rate works like this = four congos sharing a hall, 3 english language with 110 publishers each and a smaller foreign lang congo with 70 publishers : Total upkeep and mortgage $1000 per month.
You could split it by four and ask for $250 per congo, but that wouldn't be fair on the smaller congo.
So you divide the runing costs by the total amount of publishers using the hall and come up with a publisher rate of $2.50 per peblisher per month. This means the three larger congos pay $275 per month and the smaller one pays $175