fenderless tractors don't scare me. I learned not to touch moving parts.. I learned how to safely touch moving parts but that's not what this thread is about. If you accidentally get bounced towards a tire, a full fender is probably safer than a clam shell fender because it covers most of the top of the tire as well as the side of the tire while the coverage of clam shell fenders vary greatly between makes and models and the protection they offer varies also. if you are in mud or poop.. waer a slicker though!
common sense here.. but id you are on a large tired tractor.. and the clamshell is the same size as a food take home container and does not shroud tire.. there is a problem. Why do you say a very small clam shell fender would be a problem when you aren't scared of fenderless tractors? Common sense would say if you aren't scared of fenderless tractors you shouldn't have a problem with small clam shell fenders.
my previous comment presumes a clamshell fender sized CORRECTLY to ward a tire. What's "correctly sized"? What the manufacturer installed or what the individual thinks is correctly sized? That would be a totally subjective call...different people could have quite different opinions of what's a correctly sized fender when considering the same tractor.
offset or not would seem to make little difference if the tire is covered. How much of the tire is covered is the question. It varies greatly from tractor to tractor and between makes and models.
in my truck i drive to work in.. i set closer tot he left front tire than the right front one. I'm protected from both by the cab.. so distance to a warded tire seems to make no difference. A truck cab has absolutely no bearing on the topic of this thread. On a tractor however sitting closer towards one wheel means there is less distance traveled before you are against the fender and possibly the tire also whereas the same distance on a tractor with a centrally located seat will likely not bring you into contact with the fender. On some tractors with an offset seat, the operator sits almost overtop the tire.