The shared expense formula, in my opinion, is the best approach. The only reason the shared expense formula exists is because some parents decided they weren't going to pay their half of everything, abused the provision, and so the state committee stuck it to the paying parents. The kicker is that both parents "should" agree to share the direct expenses. Most who receive child support see the dollar signs and disagree to share direct expenses in order to gain a higher child support amount. BUT, the parent who receives support is fully responsible for all costs (all school, all activities, all sports, etc.). The downside to this is that one parent is deemed the "paying" parent and the child will always see that this parent is the one who buys everything. It causes psychological bias toward the parent who buys everything, which I think is wrong. That's why the shared expense formula is better.
There is also a benefit to you in your financial matters. You have to claim that you make less income when you apply for a loan, because child support is subtracted out. Yet they don't ask if you have a dozen kids at home to feed, they only ask if you are court ordered to pay child support.
Also, you might want to think about your definition of shared residency. The courts only recognize overnights for some reason, so you need to consider this when asking for shared residency treatment.