Am similarly challenged in the head department – long front to back approx 59cm – helmets are a nightmare- have tried lots as like you was looking for something with a bit more coverage than my v. old Giro E2
As per other posters Giro seems to be the best for this head shape – the hex/xar were comfy as was the feature – I was worried it would be v warm though but probably offered the best coverage.
With other brands I tried (POC, Bell super, laser, kali) as the helmet got bigger it got significantly wider and didn’t feel at all secure on my head wobbling from side to side at the slightest provocation. Obviously the mushroom effect was also troubling.
Ended up with a fox flux – good fit and cheaper – worth a try. The go faster spoilers/fin things are an added bonus.