Hi,
I can't help specifically, but just as a general point:
If you're using a full frame lens on a cropped-frame body you can actually use a more intrusive hood than standard, if you want to, because cropped frame bodies don't use the edges of the full-frame image circle.
Also, even full frame cameras can differ a bit between brands and fittings, and cropped frames can differ much more. I suspect (though i could be wrong) that sigma 'may' not have a different hood for each camera brand/fitting, instead perhaps going for a widest-fits all approach. If thats so then customising a hood to the a specific camera could also help for that reason too.
I've seen posts elsewhere of people buying longer hoods (meant for longer lenses in the same brand and with the same hood fitting/diameter) and shaving them down to fit exactly the angle of view of their camera. They seemed happy enough with the results but i guess you'd have to take time over it, and take it off the lens before diving in with saws and files! Maybe not an approach for everyone..
Kevin
PS and of course zooms will always have challenges in this respect, as their hoods must fit the widest angle of view and so will be far from ideal when you then zoom in. If you find yourself using the long-end of the range a lot then you could consider getting/making a hood just for that focal length, or else some sort of adjustable flap setup (maybe mounted on a filter holder or something) to account for the zoom at any length. Guess it depends how much effort you want to go to really, and if your type of photography allows you the time to fiddle about with hoods for each composition.