L&R front speakers - Perpendicular or Angled??

[Jordahn]

All diagrams and pictures I've seen of a 5.1 surround sound system have shown the left and right front speakers to face perpendicular to the viewing area of a home theather setup. I normally have my speakers angled towards the sweet spot and instead found it to sound a little better. I know the important thing is how it sounds best to me, but are the left and right front speakers made to be positioned to face perpendicular to the viewing area? If so, maybe I need to tweak my setup even more to possibly get better sound by having the speakers perpendicular instead of angled. I have a +five year old SONY HTD-DW840 which includes the STR-K840P receiver. Opinions?