Granted, I’m new to ham, but I haven’t seen a DIY j-pole like this with an element in the middle tuned for a different band. All the diagrams I’ve seen show that the 1/4 wave element (the parasitic element?) is supposed to cancel out the bottom part of the 3/4 wave (driven?) element.

At first I thought the 70cm band element was just for running a second coax connection that you’d swap between, but it has no connections. Furthermore, my reading on j poles says that they’re supposed to be sensitive to metallic stuff around them, so an extra element would seem to interfere.