If you are only allowed to install a 6 foot dish, it is capable of receiving most MPEG2 transponders. If you could install an 8-10 foot dish, then most MPEG2 and MPEG4 channels would be received. It makes no sense to go with a 6 foot unless you have no other option.
The challenge with using an undersized dish is that the wider beam width does not attenuate the signals from the adjacent satellite. You may pick-up enough signal with a small reflector to provide a reliable signal lock, but often the next-door satellite signals wash out the tuned satellite signal. The satellite footprint charts are only predictions of the estimated signal strength of a transponders fully loaded with channels and running at full power. They do not take into consideration that most transponders are not run at full saturation or for what signals are going to interfere from the adjacent satellite.