You only have to block off the mentioned rows if the aircraft is not full and below a certain pax figure, as mentioned, when rule two is used this is to increase the range of the stab trim to allow for a take off within the AC limits, this may not be needed if Ryanair used the aft cargo comps, but due to the restrictions in the 25 min turnaround it is not possible to get the equip needed for this exercise, therefore only the front two tend to be used causing them to position the walking payload...
Hope thats a bit clearer for all?