I've never seen it make any difference which way the lnb was oriented, facing back or front. By angle bracket I assume you are refering to the waveguide elbow. Most people leave the elbow on as it helps the lnb remain withinn the feedhorn cover. I sometimes don't use the C band elbow myself, I've found that you can sqeeze just a tad more signal without it. Although probably not enough to notice on most signals.
The C band lnb will only mount 2 directions, either way the waveguides will line up. A KU lnb however you have to watch and make sure the waveguides are oriented the same way, as it's possible to mount them sideways.