!!! I have made the switch to the BOA® Fit System!!!
Mid-foot cleat position is becoming more popular. Many people swear by it including Joe Friel from the "Training Bible" https://joefrielsblog.com/more-on-cleat-position/
I have had a lot of success in helping riders with metatarsalgia or just fore-foot discomfort on long rides. By moving the cleats back you distribute the load over more of the foot. For Triathletes, it can save your calves for the run. This position is also thought to increase efficiency. Check out the link to Joe Friel's website to learn more.
I calculate the normal cleat position to be at 95% of the measurement from the measurement back of the heel to the center of the 1st metatarsal joint. Mid-foot is at 73% of that measurement. I came to this by measuring Joe Friel's old shoes. That cleat calculation has worked really well for everyone.
When the cleat is moved back to the mid-foot position the cleat radius no longer matches the sole radius. This part of the sole is flat. Note the gap between the cleat and the sole.
I provide an adapter to go from the cleat radius to the flat sole.
Pictured is the Look Keo adapter. I also make a Shimano and a generic adapter.