Even if two different aircraft have the same space constraints for the hook (which is a pretty big if), they have different mass and deceleration characteristics (i.e. minimum and maximum approach velocity) during landing- changing the force exerted on the hook. Designing a lighter hook for the lower loaded aircraft is VERY desirable for high tech fighter jets- every ounce saved is better range, better agility, etc.

As far as the little lip at the very tip of the hook- it looks to me like the initial design was trying to minimize any risk of digging into the flight deck and causing damage- this is just a guess though.