Genetics questions early on a Saturday!
It is not as simple as that:
See, rose comp is RRpp. Pea comb is rrPp and you can get it from different parents. You can have an Rrpp rose comb parent and then have pea comb offspring with the correct mating.
If you notice, single comb is Rrpp, so there is a single dominant R and you get straight.
This chart has a typo. Single comb is rrpp (if you look you can see the box they have it in even is under the rp x rp cross, so impossible to get Rrpp.