Many of my friends and I all struggled with the touch the top of the plate thing, too, putting the plate much too high on our backs. We struggled to reach the valves because, as you said, you need to look up to be able to reach them effectively, and the manifold was pushing our heads down.What AJ said. The plate is too high and it appears your shoulder straps are too tight. I too was a slave to the “just be able to touch the plate” problem. It’s a generalization that I don’t think works and leads to plate being too high.
When reaching back besides elbows forward, don’t drop your head. Everybody wants to lower their head or bend it down because it naturally feels like it would help. In actuality due to our biomechanics it actually makes it harder to reach the valves
It also made it hard to swim in trim because you couldn't see in front of you because of the isolator holding your head down. Coupled with the tanks being to high on your back making you head heavy and unstable in flat trim.
It's bad advice that needs to go. The reality is a better starting point for the plate is as low as possible on the diver while still allowing them to get to the valves.