they are playing games, there's no reason that 4.2 was not fully rented out and then 6.5 some are rented out.
Rate is fixed for the qty of miners, you can find this info on thier website. If you have less then 10 miners (and no tokens) you will pay highers rate, if you have from 10 to 50 -lower, etc. if you have more than 100 - the lowest.
GW has old customers who worked with them before ICO, and most of them I guess have more then 100 miners, that is why it's diffucult to rent our all tokens at high rate. Renting is made automatically, and you can't choose what to rent out and to whome. Rather complicated i know. But when they launch farms at full speed (in a few months i hope) all tokens should be rented out i guess.