It makes sense to me you can see the difference in all 6 exposure segments. The method is fine as I said before. We just need to trouble-shoot how you are doing it.
Now that you say you are using art paper for your blocker, I don't know, I think Thomas may be on to something. It could be some light is getting through. Try using two layers and see if that helps. I'd also suggest making them substantially larger than the sheet of photo paper to make sure you don't accidentially end up uncovering part of the paper without realizing it while making the test strip. It also lessens the possibility of stray light getting under there.
Usually for a blocker (also used for burning and dodging), people tend to prefer heavier stock, like 4-ply mounting board in thickness. Illustration board, that sort of thing works well. It should have a flat/matte finish on both sides. It is also helpful to have the side facing the photo paper be a dark colour or black. Most art stores sell this sort of thing with white on one side and a dark colour or black on the other side. That is ideal. The white side faces upward so you can see what you are doing, while the black side faces down.