And maybe the patients rather large nose
Heh - I fall into that category.. A fairly large, and unfeasibly un-bendy nose makes a lot of helmets with any kind of nose/face protection fairly uncomfortable - and due to them constantly contacting or pushing on my nose won't give an awful lot of protection if anything hits there with force - but even so, its a lot better than no protection at all. Just needs to be fitted/padded so a knock on the noggin doesn't push it into your nose.
And following on from what Paul said - I agree totally that the risk of injury is increased dramatically when fighting against people from other groups with other styles...
We do headblows in our group - and in 12 years of re-enactment with weekly practices in the two societies I've been in, I have never had more than a minor cut/bruise (and its been a long time since I had one of those). But the vast majority of that time has been only fighting our own group members.
And strangely enough, most head injurys (all minor) have occured in a time before we allowed headblows. I really don't know if this was due to combination of more head protection and knowing how to defend the head, or moving away from battle-related shows to a more 1v1 based show - therefore removing the risk of injury from ppl you're not fighting (if you follow).