When I got my first pair of 105s in 1990 or so I could really feel that back cage but now I don't even notice it, even with Chucks on. I feel the pedal offers a lot more support to flexy thin soles than say the Sylvan.

Running shoes are the best in the 105s, though. A little strap pressure will press the back cage into the sole a bit and kinda lock my shoe in without creating hot spots on my feet and the soles are thick enough I can't feel the back cage in my foot with the strap cinched a bit.