I felt like my PN-NCLEX was harder than RN. But, I think it's because you don't know what to expect the first time.
I also studied things that I felt weak on LPN. They didn't even test me on those subjects. I thought the RN one was weird as they also didn't ask me any labs, drug calc, any meds, or EKG strips. Mostly priority, assessment, and delegation questions. I thought there is no way I can pass not being asked any of those topics. Turns out I was wrong.
Passed PN at 85 questions -1st try
Passed RN at 75 questions -1st try
So, I don't think they test LPNs harder to answer your question. I just think, it's new info when your an LPN.