Bruised toes due to shoe fit?

Hi All

I took up fell running a couple of months ago but in the last couple of weeks i've done some longer distance runs in my fell shoes, a pair of More Mile cheviot Mk1s, and i have started to develop sesamoid problems with severe bruising around my toes -in particular the side of my big toe on my left foot.

When i bought my shoes i followed the same principle as for road shoes - that you go a half size bigger (some people say a full size bigger?), to allow space for hot feet to expand. Is this right though? I'm now thinking that the extra space in the toe box is allowing my feet to move around too much, especially on steep descents, and i'm thinking this could be the cause of the bruising.

I'm a size 9 in normal shoes, usually a 9.5 in road trainers (I usually buy Nike) - I know its different for different makes and models, but as a general rule should you go the half size bigger or not - or to phrase it differently, should you allow space for movement in the toe box for hot feet to expand, or is it better to have a fit as per 'normal' shoes rather than road running trainers?

Any thoughts gratefully received...
Tid