I don't think the ratios are set in stone. I've gotten flavors at different ratios in different orders (e.g., 70/30 in one order, and 60/40 in the another).
The Aroma line is PG-heavy (but not VG-free), and the Red Tail line is VG-heavy (but not PG-free). Beyond that, I suspect each batch is fine-tuned to achieve certain qualities regardless of the ultimate ratio. Kinda like a winemaker.