Hi Guthwine!
To be honest, I don't remember if the pic was taken in the final position of the cav. (probably yes), and it was moved in the heat of the battle...
In any case you are right it seems to be in the front arc. If we were playing WMA, yes, but in WMF rules, first draw the shortest straight line and see from there remaining stands fall one side or another. WMF page 33 Diagram 33.2
Looking now the pic it seems the shortest line is corner to corner and the rest of the cavalry stands are on the right half, flanking?? Not very sure of this...