Doug,

I can't answer properly to your question, but I have found two clones of
Hippeastrum aulicum here. The one in my photo is the 'robust' one with flowers
of 20cm (almost 8") across of a vivid red orange. The 'weak' one has flowers
of 12cm (barely 4") of a paler colour with more green. It's not a matter of
cultivation, because the 'weak' one grows well, but it is just smaller.
Probably there's a bit of variability in this species.