This is a problem across the races not just FLM. I had a similar moan at Liverpool half, where they only had L and XL left. I took L and it was RIDICULOUSLY big. I'm 5'7 and a size 14 top because I have boobs, but no way could I wear it. I felt cheated. I actually would rather have a t-shirt than a medal. Wearing your medal after the race makes you look a tit, but a t-shirt (especially a tech tee) would be useful.
Even worse than that, some smart-mouthed git suggested if I run faster, I might get a t-shirt that fits!
I should have gone with my instincts and smacked him in the gob.....