byond decoder uses both high and low LO(local oscillating) frequencies, currently all SD channels are allocated to low LO, and HD channels to High LO frequency

my guess is that the flat's shared dish usually provide low LO only, and High LO is disabled

so technically if byond is connected to flat's dish, you can still view SD channels

if shared dish does not have device to disable High LO, your byond tuning to HD channel will interfere with other astro viewer watching SD channels, may be that is why your management said byond is not suitable for shared dish