OK, so I finally got a look at this yesterday...what I can see is that (with the TPS disconnected and the servo in the Hi position) is that the "body" of the RC petal is flat and in line with the port edge but because the petal is cup shaped the edge of the petals rise up into the port at the mouth of the outlet...if that makes sense.
On balance I realise that the port is oval and the petal is not as oval, so its edges look to block the outlet a little...would I be right in thinking that this shapes the charge as it exits the barrel?

Honestly I preferred my RS125 that just had a carb and a spannie !