Although looking at the hardware this may be obvious, the data points to what looks to be airflow restrictions.
Due to that, there is an excess of heat being produced and as such can't turn it up a hell of a lot or it just knocks.
I think the sweet spot on my combo is somewhere around 12 psi even though I can get more into it by pulling timing but as you know that just makes it worse.
It'll make the boost, I've seen plenty in the middle and still a lot up top when tuning but it can't handle any timing when wound right up.
I think this points to an exhaust restriction more so than intake.