I've been playing with Luna/invisible sandal design for a while. My problem has been the lacing between the toes, just can't get used to that. Thought it might be the use of shoe laces so I tried 1/2 leather strapping, that didn't help.
Next was look into different lacing options. After looking at various sandals on the market and experimentation I came up with something I like. I've always liked Teva strapping position and figured out how to with one piece of material. The prototype was done with shoe laces, then I moved onto leather but it was too stiff around the 5th toe. Looking for an option I found Luna sells supplies, so I ordered the elastic strapping. It worked like a charm and has the benefit of not having to be untied to get it on and off.
This configuration works great! Have done some light running and foot stays put, no sliding forward due to the strap at the front of the ankle. I was worried the front edge may catch the ground at toe off but that has not been a problem
Is the knot on the outside of your 1st toe, then?