Your other option is M performance diffuser but a replica one from ebay without carbon fibre. I bought this one & the fitment is great. You can see that the oem 540i exhaust tips are smaller. Now I'm looking to get the m performance tips which will fill up the gaps in the diffuser nicely. The M550i tips are designed to fill that gap.
They seem to be out of stock now but ask them when they will get some more.
https://rover.ebay.com/rover/0/0/0?m...2F192629463859
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2018 M550I Xdrive Alpine White on Cognac Leather, Premium Enhanced Package, Drivers Assitance Plus, Remote Parking/display key, massage seats, 21 wheels style 629 Black Chrome. M performance brakes in blue, M performance carbon fibre diffuser, m performance side skirt extensions, m performance front lip. 45% tint, roof wrapped in gloss black.