The SFF label shouldn't be applied to cases using half-height slots. SFF should be considered a specific shape for a Flex-ATX system.
Flex-ATX is an older standard on which most SFF cubes and dictionary-sized PC's are based on.
If you want a low profile or super narrow case, I'd still go Micro ATX, rather than Flex ATX, it will give you better motherboard choices and availability of standard parts.
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