Track Entry Rules

Anyone know how to customize track entry rules in cadences? For Positive and Negative tracks I have the same three options:  

• Email Reply
• Email Open
• Email Link Click

We've been using Sales Engagement for a little over a year now and are ready to start experimenting with with cadence steps that are more relevant based on target engagement -- but if I can't customize the track entry rules, I'm not sure how this is of value especially for the negative track. Thanks!