Now, the ratio itself isn't a problem. The issue is the rest of your truck's suspension and how beat to hell it all is. The condition of bushings, springs, shocks, and other components of your F150's front suspension will all play a role in determining the final ride height. This means that truck's with a good bit of miles on them or that get thrown around on the regular will see slightly lower ride height gains than a truck that's just rolled off the factory floor. So, the answer to what height spacer is actually level is a bit more complicated then it first seems.
We usually recommend just sticking with a 2" leveling kit, however, many 2" kits don't provide enough lift to get a "dead level" look on trucks with a lot of miles or have really been flogged around both on and off the road. For F150s that have seen some use, a 2.5" leveling kit will be a better choice, and are even a sensible option if you know you're going to hang onto your truck for a while. Your suspension is going to settle and break-in eventually, you know.