Often people get hung up on the label of who gets physical custody.
Legal Custody = who gets to make the big decisions in life - health, education, religion, etc. Most of the time parents will share joint legal custody.
Physical Custody = who the child lives with the majority of the time.
Often it makes the most sense to label someone as having "sole physical custody" however what you really should pay attention to is the amount of visitation that the other party has. If you are getting 40% visitation then honestly your ex having the label of sole physical custody does not make too much of a difference legally.
The main thing to pay attention to is the amount of visitation time you get as well as making sure that you address the holiday time, school vacation time, and tax ramifications of custody time. Tax wise, unless you agree otherwise in your court order, the person who has 50.01% of the custody is the person that gets to claim the child EVERY SINGLE YEAR. So make sure that you also address taxes in your agreement. Typically parents who share custody (60/40, 50/50, or a similar split) will agree that parent #1 claims the children on even years (2012, 2014, etc) and parent #2 claims the children on odd years (2013, 2015, etc). Also if there are 2 children sometime parents will agree that every year each parent claims one child.