I think there should be something that could be changed in the BCON files in SimPE but I've never fiddled with them. Some sims are more active than other's I have sims that go days without utilizing ACR even though they are in proximity to their one and have plenty of free will time in order to do so. I have other's that get active more than once a day, even if neither timer should be kicking in yet. Age/personality/aspiration all tie in I believe.