...first, unless your left leg is both your dominant one, and there is a significant difference in how much downward pressure you can exert with each leg, I don't get why always the left crank arm.
Second, I only use pedal extenders on a couple of bikes, where there was no other way to gain enough clearance for the toe straps I use to clear between my shoe and the crank arms.

Third, I'm not certain what you mean when you mention your out-tuned feet" ? If you are pedaling your bicycle like this (heels pointed significantly inward, toes out), you will eventually cripple yourself if you ride far enough regularly. There is this whole art and science to adapting your own unique foot anatomy to the pedals that connect you to the bike. Pedal extenders are not the way you want to do this, except as a last resort. They can be used successfully to widen the Q factor everyone is always talking about, for people with wider pelvic structures and a natural spread between the feets that is on the wider side.

But yeah, I guess the pedal extenders might be contributing to this. I can't tell you much more that might help, because it's not something I have personally experienced. If you want to continue using the pedal extenders instead of trying to figure out a different way to alter your foot position in the pedal (it really is something you need to experiment with...that was the only way I finally figured out my foot pain on long rides issues), I guess there's always the option off finding some old bike with a cottered crank. Properly seated, those crank arms are on there for the duration.