I assume your question refers to a sitting position in a kayak and not the proper stance for planing a rolling bevel on a wood strip.

In a kayak you want two things: comfort and firm contact with the boat. You knees or thighs should make contact with the deck of your boat. You knees are likely going to be splayed out to the maximum width of the boat, unless it is VERY wide. If your knees are not out near the sides of the boat if is hard to control the boat around the roll axis.

Your feet need to be on whatever foot support system you have in your boat. Side-to-side spacing doesn't matter as much with your knees. Fore-and-aft positioning is more important. Your ankles should be close to a neutral position. If you can't lift your feet off the foot pegs to stretch your legs, the fit is too tight. And if you're stretching to reach the foot supports with your toes, they're too far away and you won't be able to maintain a proper upright paddling position.

It's time to go paddling.