Yes, the fuel contract is only for fuel purchased at your hub. The outstations are all at pump prices (or your hedged price). But the fuel bought for the plane at the outstation is always charged to that plane's base, which is why you take the base's monthly number and divide by two.
Here's my formula:
Monthly fuel cost at that hub, divided by two.
Multiply that number by the discount. So if the discount is 5.8%, multiply by 0.058 to get the discount.
Then compare that number to the monthly fee for the contract. If the discount > fee, it's a good deal. If the fee > discount, it's a bad deal.
Protip: If you're in growth mode at that hub and a fuel contract is a slightly bad deal but it's for a long term (3+ years), jump on it before you schedule any more planes. Because your fuel cost at that hub is going to grow dramatically and that slightly bad deal will quickly become a very good deal for several years. If you try to get a fuel contract later the deals likely won't be as good.
Protip #2: The "renewal" deals are always crap. Let the contract expire and then a better deal will show itself.