Sorry Reg, it's not that and I believe LM has covered all those "angles"
Sorry LM, it's not dihedral either, I think that leaves only one option, but keep looking, you're in the right area!! I recall that we had a similar one a while ago, when that little PITA ChazChaz was about!! Shouldn't really say that should I, but he won't mind....
Edited to say I'm off home at 7:15 and will put my light back on when I get there (about half an hour).