Thanks for the explanation, T-Mar. I've just found some photos of racers from the 1950s-70s that clearly show the foot clearly not being in contact with the clip, so I have no reason to doubt what you are saying! It makes sense from a technical perspective.

However, I do not agree about the issue of discomfort, assuming that a rider does not actually apply regular forward pressure on the clips. I personally do not ride with cleats, so having the front of my shoe contacting the clip is how I know I'm in a good spot over the pedal. I simply let my foot rest in a position where it can no longer slide forward, and I'm aware that sometimes it begins to slip back again and I then easily correct myself but pushing forward momentarily until I touch the clip. After being out for upward of 50-75 miles I've never feel any level of discomfort in my toes or feet.

I had presumed that clips, especially of these early sorts without the aid of straps, would have been used similarly.