When dealing with equity, especially at private companies, expect the data to be terrible. Get more than one set of data so you can have a reasonable range for the terribleness. Then do your process in reverse. Instead of looking at the market data and determining how to fit people in, look at your people and determine what you are trying to accomplish. Then determine what levels of equity and types of features will help you reach your goal. Finally, take a look at the market data and determine if you are, based on your needs, within the right range of accuracy.