Some background knowledge?
knits and purls “curl” the string the opposite way to each other as you know.
when alternating knits and purl or changing from one to the other, the knit stitches appear to be “higher up” than the purl ones. That makes them overlap. Depending on the yarn, the needle / yarn ratio and so on, the overlap is differently large. But in general you can expect to have an overlap of 0.5 stitches.
So when you alternate one by one k p k p k p you pretty much only see knits and the purl stitches “fall between them”.
or you alternate k2 p2 k2 p2 k2 p2 and so on, the ribs of knit and of purl overlap by about a half stitch on each side so you see some purl between the knit ribs.
the more knit you do before you do (e.g., but not necessarily) the same amount of purl, the less places of overlap you will have.
When you pull on apiece of ribbing (sideways) it stretches out and you see all your stitches. The more overlap the more stretch.
The most well known is k2 p2 but for baby clothes for example I like using k1 p1.
Just try with your yarn and needles. You will see!