Increasing rise as well as length?

Hello! I need assistance from those with more experience. Normally when making a pant pattern, I will go with the size that pertains to my child's hips/waist measurements and then add a bunch of length as per instructions given on this blog. However, for my son, this means a pattern size of 2 or 3 and then adding enough length for his 6 year-old frame. (Which is a lot as he is tall.) This works out quite well for the most part, but I am worried that I need to be giving him more room in the rise. Yes? No? What is the best way to determine that and then how would I alter the pattern piece?