Never Get My Turn To Win The Buy Box

Hi! I am an Amazon seller for 16 months so far and never could wrap my head around how the BB rotation works. I am one of only FBA sellers on the listing of a product with 50 monthly sales. We both sell at the same price yet It’s been a week and the other co-seller still wins the Buy Box. The only thing I noticed is the inventory, I have only 13 units and they have 270 units. What do you guys recommend me to do? I have 2 things in mind: 1- go down with the price and this will cut down the profit considerably. 2- send 100 units to my FBA inventory to be eligible to the shipment optimization. Not sure if this is wise, I believe I would sell 25 units/month at best if the buy box rotates evenly. IDK I need advice on that or any other way to avoid losing money. What do you guys recommend?