Yes that is right. The farming rate will be determined by the network as a whole. So we should be able to see what it sets and maybe publish that over time. It will tell us if we ask it 
I see it something like (made up numbers for example)
Day safecoin per 500Gb per day
1 1000
100 800
1000 200
So as the network grows the space is cheaper, but if safecoin value goes crazy (it might) then it may look like this
Day safecoin per 500Gb per day
1 1000
100 20
1000 3
OF course it could go the other way if the network needs more space. In that case it will increase farming rate, and take no notice of outside price, it will notice the oversupply if its too generous and reduce it quickly or the other way around. In essence balance of rate will be the networks job, but in doing so it ensures space/cpu/bw etc. are available. The price just means more folk will farm if its valuable and less if not, if it is less attractive the supply of space drops, the network increases rewards etc.
Hope that is what you asked