I found that the most important thing is, not that there is a long extender, nor even increasing Q factor, but rather ensuring that ones toes are rotating away from the bike. Extenders encourage and facilitate this outward rotation. But so does a thin washer. I am currently using a 2mm washer on my right pedal axle and attempting to rotate my right heel inwards, towards my BB just a little. This has been enough (together with various types of exercise) to reduce or almost eliminate, my knee pain.