A slight design flaw

I bought this bird feeder to replace one that had been chewed apart by the squirrels. It is a supposedly squirrel-proof model. The outer cage is atttached by two springs and "floats" over the inner tube. The cage has metal leaf shapes and it can be pushed down by extending the springs until the openings are covered by the leaves. If a lightweight bird lands on the perches, nothing happens, but if a heavier squirrel hangs on the outer cage, its weight is supposed to stretch the springs and pull the cage down to block access to the seeds. Well, that's how it's supposed to work. The problem is, the springs are so stiff and strong that my squirrels don't weigh enough to activate the squirrel-proof function. Maybe if they steal enough seeds, they will gain weight, and then. . .