When we separated it was agreed that we would have joint/equal parental responsibility. In short, the kids would spend the same amount of time with each parent and the cost for trips, clothes, school things split equally. This has been working OK.
Each parent has the children for 15 or 16 days a month with some flexibility (we're keeping things amicable). My divorced parents have the kids for a sleepover once or occasionally twice a month so I may only have the kids 12 or 13 days actually 'sleeping' at mine but they are with my family and I am responsible for them.
The question is, could the OH argue I am not having the kids 'sleeping' at mine for exactly half of the time and seek child maintenance payments? It may not be an issue but the kids mentioned they do not sleepover at their other grandparents anymore, which is most unusual.