Yes it should be shaped for a perfect fit into the groove. The lid clamps it down to form a tight seal.

Imo I'd take 1 of the 0.5mm spacers out from the needles....1 mm is a lot and it could be letting to much fuel in as the revs drop..just a thought

Thanks for all your help MadMotoUK, magg and richyrd5. It is now idling fine. It was the second spacer on the needles as richyrd5 suggested. I checked them and all the non oem ones were 0.6mm and not particularly flat either, the oem ones were 0.5mm spot on. I took the 0.6mm ones out and binned them. The genuine air filter now fits better after being fitted and some heat from using the bike so all good. Here's a couple of pics from the test ride on Sunday

https://ibb.co/Cvh9Thn
https://ibb.co/VQRFkPG

Glad you got it sorted..lovely those seed colours