I premix my PG/VG. I have 3 different bottles of different ratios. I do not worry about the math for the final PG/VG ratio. It is like squabbling over a penny while quarters are rolling by. I'd rather spend my time at the mixing table mixing rather than worrying that my final PG/VG ratio is actually 68/32 and how to correct such a meaningless number.
I worry about nicotine content first and taste/flavoring ratio next. How much the flavoring throws off the PG/VG ratio is like arguing that the shade of brown in the kitchen doesn't match the shade of brown in the bathroom. I don't give a flying fig, it's brown. (I'm sure there will be an interior decorater along to tell me how it matters that shades of brown match in two completely different rooms, but I still won't buy it.)
I'm curious, what's your preferred nic level? source?