What the table is demonstrating that regardless of higher K, flowering is still reduced under high P concentrations.
Adding extra K not only increases the K/N ratio but effectively reduces the total N given to the plant - IF you don't increase the concentration of the solution you give to the plant. Optimum K/N solutions in commercial hydroponic set ups in Holland have found a K/N ratio of roughly 1.5 to be best for a wide range of crops including flowering ones. The K will help to regulate (reduce) stretching (and in our case bloating of the cacti) from the N. You could even consider your last 2 feeds of the season to be pure potassium sulphate and zero nitrogen. It will help to harden the plant and keep it compact as the light levels and temperatures fall.
Let's remember what the cacti see in habitat.. Low N and/or high K. 4, 6 even 10 times as much available K as N sometimes!