When I think of an inverse curve that indicates rebound, I think of one with a lot more variation in the numbers - lows that would be good nadirs, happen at PS time, and at nadir time there is a 300-something - so still 200-300 points of dip/climb. This isn't what is going on here. He seems to have high, flat numbers with little movement.
Without seeing what he did on lower doses of PZ, it's hard to know if the high flat numbers are not enough insulin or too much. Since you are not yet near the old PZ dose, maybe continue to raise the dose until you see lower numbers and a "normal" curve. Jut make sure you give plenty of settle time and don't raise until you have at least a mini curve to show where the dose is taking him.