Actually, I think we're just talking about different aspects of the wonderful world of cables. Usually cables cross on the knit row which is the right side (RS) row.
If you're fourth row isn't a cable cross and the directions are just "..knit one, purl four, knit one..", then go ahead and do just that. Is the purl four the wrong side (or back) of the cable? If you could provide a link to the pattern or the pattern name, that would help too.