If the SF is like the Omen, the manual says as long as you can slide a standard CD case between the speaker and the floor you're fine.
If you're using the carpet spikes I believe the gap will be greater than 1 case, but the way I interpret the instructions that is OK. If you use the bare floor studs and not the carpet spikes you can get the gap lower than 1 CD case (on bare floor) up to more than 2 cases.
FWIW - I found that gap to be a pretty big adjustment knob. I have my Omens on boards with the carpet spikes.
If you're using the carpet spikes I believe the gap will be greater than 1 case, but the way I interpret the instructions that is OK. If you use the bare floor studs and not the carpet spikes you can get the gap lower than 1 CD case (on bare floor) up to more than 2 cases.
FWIW - I found that gap to be a pretty big adjustment knob. I have my Omens on boards with the carpet spikes.