Looking a little deeper into this and my pictures I took during the build, all of the pistons have slight witness marks on them from the inlet valves. So this piston to valve contact was happening before I even owned the car.
At the time I dismissed it as I just thought the car had a mild over rev at some point. It was running single valve springs and stock valves that I was going to replace anyway so I didn't think any more of it. Another assumption that's cost me.
So bottom line I should have measured when I built it but there was just far far too much advance done on the original tune long before I bought the car.
Here's the pics, you can make out the marks from the valves on the pistons, just below the cut outs.
Pretty damn conclusive I'd say.