Do they till request a donation (that is, payment-per-seat) when the convention is held in a JW assembly hall versus a worldly venue?
Hell yeah. They run through the convention accounts just to guilt trip people into giving.
It's how halls like the Surrey Assembly Hall at Haysbridge in the UK can afford to
donate almost half a million pounds to the WTS and still have almost £5m in the bank.
See the accounts online here.
http://apps.charitycommission.gov.uk/Accounts/Ends09/0001090209_AC_20150831_E_C.PDF
I've tracked this for a while and the income has regularly been approx double the expenditure. They could ask the congregations for half the amount they do but this is a neat way of generating income for the main org.
Now add another 10 or 12 events in a year if they moved RCs there, into a building that is paid for, a building they own, a building they don't have to put the outlay into that they do for a stadium.
I bet half the bean counters actually want a reduction in numbers (aka "love of the greater number cooling off") since it will be the hard core left and therefore easier to fill WTS venues with a higher ratio of fee paying punters.