From my outsider point of few I wouldn't think either parent would be accountable for any past due child support unless there was some kind of judgement ruling so. The fact that both parents signed 15 years ago for no child support and neither parent has since motioned to change that, I couldn't see a court ruling in favor of either parent for past due child support. It also sounds like there is somewhat of an agreement to pay for direct expenses. For actual shared physical custody (number of overnights is nearly equal) per the pre-2008 guidelines, the amount of child support was rather small, but both parents were then required to share direct expenses. In 2008, the 80/20 rule came out which was terrible on the part of the committee and should have never been released. But thanks to the exhaustive efforts of a few parents informing the committee of the size of problem they created, the committee decided to implement a new shared custody child support method. Sharing expenses is no longer required, but since you already have an agreement to share expenses, you probably should be basing any numbers you calculate on this fact because there is a filed document which states that expenses are shared (as I read it).
Back to your question - Unless there's other information which hasn't been posted here, I could only see a judge changing child support to be consistent with the guidelines at this point, not ruling for any arrearage. But, since things are getting hot in the oven, you may want to keep copies of every thing you've paid for in the last year and from this point forward.
Sometimes hearings go terrible, though, and not at all the way people have planned in their mind. Sometimes if you wear the wrong color shirt, or if you don't part your hair the right way the judge thinks you should be punished. A judge has a duty to uphold the law and that is it! So, keep in mind what a judge can and cannot do here. I hate to say it, but unless you're well versed in KS statutes, the child support guidelines, and the your local court rules, you may want to call the KS bar association and ask for your $20 30 min legal advice session. This is a service that the KS bar offers to promote attorneys and give them new leads.
