I had the same problem with my 2 Ragdolls. They have so much thick wooly type hair, it was impossible to find the skin!

I just got someone else to help me while I did it. We parted the hair as best as possible, I made sure the tube touched the body and that seemed to do the trick.

It's always easy if your cat lets you do anything to it, which mine do. They didn't even have a clue what I was trying to do and they sat still the whole way through.