I need to validate comps but typically independent board members receive equity compensation that is in line with what you would give an individual engineer you would bring on. There may be data here: https://drive.google.com/open?id=0BwaXE7ECjAJHUWlwczBfUXBGZGc for you to benchmark.
For ex: If you're doing $4-5M in revenue, I would say a common independent would receive .1 to .5 percent beating over 2 years depending on the status of the individual.