My question involves child support in the State of: Oregon

I'm wondering if anyone has any first hand experience in paying Child Support to a college aged child, 18-21 in Oregon. I had a friend recently tell me she went to the CS calculator, and input some information to get an idea of how much CS her husband will need to continue to pay to her step-son, when he reaches 18 soon... assuming he'll go to college. She was SHOCKED, to say the least, that his support will more than double?? I thought, that can't be right. I have a step-daughter who will be 18 in a few years, and assuming she'll go to college, I went to the CS calculator, and found that the calculations I input, seems to increase my husbands substantially also. Doe CS really double or more for a college aged child??
Can anyone share their story of CS for a college aged child? Also, we know that the custodial parent is obligated to pay CS also for the college aged child ... what percentage are they responsible for?
Plus ... my friend believes her step-son will be doing online college courses. She couldn't find anything (nor could I) saying that the adult child will or will not get CS if they do online courses only. Does online college count?
Just looking for a heads up from those with experience! Thanks in advance for your time.