I don't run a shop and never have, but business is my "thing". So please, understand my input is just trying to help, but isn't based on any experience specific to this field.
Your head hancho in the kitchen is a critical position. Overseeing the others, performing quality control, etc. This is your product and is what brings people in the door and makes them want to come back. Also, this position is critical in profitability -- monitoring that the staff are weighing ingredients, preparing the right quantities of to minimize waste, etc.
I would consider very strongly paying this position in the form of salary plus bonus based on your business overall profitability. Maybe you factor out overhead like leasing and equipment costs, and calculate what the profitability of the actual food products needs to be to make your target overall profit margin. Then establish a bonus plan that if that product profit margin is met, the head gets $X in bonus, and for every 1% the target is exceeded then increase the bonus by 1% as well. I'd design it so that the bonus is about 20% of their overall compensation. Give them skin in the game so their motivation is aligned with yours --maximize profit by producing a quality product, with tight quality control, minimal waste, and customer satisfaction.