I need Advice!

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So, I consider myself to be a pretty accomplished artist. My problem is that, even with bachelors degree in art, I still have issues with accurate preportion. I've tried EVERYTHING to get my right brain in check, including the thumb and pencil trick, and stick figures, but I'm still forever drawing my head bigger than the rest of my body, or my eyes bigger than the rest of the face. Does anyone have a suggestion to improve my perception? Is preportion instinctive, or is it something that I can fix? It's VERY frustrating, and while I do eventually get it right, it takes significantly longer than I'd like. Please help!