Too Little Starch

I've made this recipe from the BY cookbook and was excited to find this version for someone on a GF diet. The muffins barely rose and collapsed after I took them out of the oven. When I compared with the original recipe, I saw that it called from 2C flour, and this one only 3/4 C potato starch + 1/4 C almond flour = 1 C of starch. Is this possible that it needs more starch? Thanks