So I did a little digging around. The stock way of oscillating the afr actually is because it facilitates a chemical reaction in the cat. Putting it in open loop under low load is going to be fine just raise emmissions. Doesn't solve the original question though.... But I view it from the physics standpoint of conservation of energy. If you are running 14.7:1 you'll be using the full potential of your fuel, same with 15:1 or 16:1 anywhere above 14.7 and you will be maximizing fuel efficiency. Butttt that doesn't account for uncertainty in things like tip in enrichment... Might be worth it.
But yes to change closed loop afr its the 'closed loop fueling target.' Mine was in at 14.47 maybe that is the stock value. I changed it to 14.7 and the car seems to hang around 15.0 mostly. Still doing the oscillating down to 14.6 or so.