@Opsimath,
I have seen problems like this when you have to compare capitals that are made up of straight lines with those that have non-straight lines.
But this is definitely vowels and consonants.
Don't try and take a round or triangular view of the letters, try another shape! You should get it now.
A little more help with the meaning of capitals in 33? Going round in circles with animals, countries, rivers and capitals. I need a thicker penny to drop here!