Does boxer exhaust valve rythm reduce exhaust scavenging effect?

[Bebbetufs]

I've been thinking about all the posts about the lack of gains from exhaust and intake upgrades. Frankly I find it hard to believe that it should be so difficult to get more than 204hp from this engine. After all Renault reliably get 197hp from the 4 cylinder normally aspirated Renault Sport engine in my Clio. The boxer is abour 20% larger. The Renault is only 2.0 liters with a similar basic on-off variable cam system.

I noticed when timing the cams on the boxer engine that all four cams are "parked" at the same time, meaning all the valves are closed for one "beat" of the cycle. Whereas on my 944 one cylinder will always have valves open when in TDC, keeping the "beat" constant

Could it be that the 1,2,3 and, 1,2,3 and rythm is decreasing the effectiveness of the scavenging putting more emphasis on other design factors of the exhaust such as back-pressure?

If this is a cause for the lack of response to exhaust upgrades could some kind of X-pipe perhaps improve the scavenging?