I'm no expert, but its possible that dip in the graph might be from the vtec crossover point not being tuned properly.

Most say to lower it with a tubular manifold and raise it a bit with a log manifold.

I have a log so I asked my tuner to raise it and the dip went away and there was more area under the curve.

Again, I'm no expert, just some food for thought, and an area of possible research for you.

Boost leak is another possibility. I'd definitely look into both.