Making it smaller is definitely one good way to go about it.
Another possibility would be to click and reward for approximations, relaxing your criteria until he grasps the idea that what you want is the position relative to you, not the foot target. It may be helpful to use a little luring or hand targeting as an alternative prompt, but you should probably try to encourage the dog to think for himself as much as possible here, rather than just transferring his dependency to a different kind of help.
It may also be helpful to take a break from perchwork exercises for a week or two and work on something completely different for a while. If you've been rewarding heavily for foot target exercises and nothing else for some time, then it's not surprising that your dog would look for the prop that he knows is connected to a reward. To break that association, it might help to do something totally different and cement the idea that "oh, okay, sometimes I get cookies for things that AREN'T dependent on finding the foot target."
ARCHMX TDCH Pongu the Insane, CD-C, RE, RL1X6, RL2X5, RL3X2 (GSD mix, b. Apr 2010)
Crookytail the Tigerwuff, RL1, ITD (Akita mix, b. Jan 2011)