Residuals are set by the financial institution who funds the lease. It's their best guess at what the vehicle will be worth at the end of the lease. Usually residuals go down (which makes the average monthly depreciation component of the payment go up) as the model year progresses. All things being equal, based on residual value and excluding rebates or special leasing programs or other incentives, leasing a car a the beginning of a model year results in a lower payment than leasing the same car at the end of the model year.
On a car like the GTO, which unfortunately has not caught on with the buying public, leasing or balloon financing (Smartbuy) is probably the best way to prevent yourself from eating huge amounts of depreciation when it comes to trade for your next car. I've seen a 3 year residual of $17K+ for a GTO. That's GMAC's guess (hedged by insurance) at what the car will be worth 3 years from now. Actually, since the cars aren't selling, it'll probably be much less. If GMAC's wrong and the car IS worth less, you walk away from the car at the end of the lease and buy someone else's 3 year old Goat for eg. $12,000 (although I've heard you may be able to negotiate the buyout down at lease end). If GMAC's right or miracle of miracles, the car's worth more than $17K+, if you like the car, buy it (generally refinance the residual or balloon) and keep it.
Rebates and residuals are, strictly speaking, independent of each other. But ultimately they come out of similar pockets (GM) and are set so that they sell cars, make money or minimize losses.
Hope this helps.
Dave