Cable risers are a sham, invented by weak-minded idiots to be sold to gullible, weak-minded idiots.
It doesn't matter where in space a cable is laying, as long as it is not in close proximity to AC mains cables.
Floors, whether wood, concrete or dirt, are not known to be significant radiators of electromagnetic or radio frequency energy. In any event, even if they were, a few inches of spacing wouldn't make much difference anyway.
Now go out and find the most expensive cable risers you can find, buy them, and report back.