The Air-cobra failed in RAF service for several reasons
Firstly the main problem was it was useless above 20,000ft - at the time they didn't have a decent turbo charger and it simply ran out of steam
The UK bought it on the basis of the performance figures of the prototype, which reached 400 mph . In service they found max speed was around 350 mph at 15,000ft - totally useless by 1941 in W Europe. The 37mm gun only carried 30 rounds and was slow firing 3 rounds a second. Because of the cockpit design it was difficult to get out in an emergency and it didn't have a clear view windscreen.
The Russians loved it - altho' most history's say they used for ground attack that's not really true - they used it as an interceptor at low levels above the battlefield taking out Stuka's , Bf 110's etc
AFAIK the engine position itself gave no real problems