I would be more focused on having a split like 30% low, 55% mid, 15% high or something of that nature. I know the idea of having each case be a range is symmetrical and and sounds attractive but from a money making standpoint it would be a big mistake. I can tell you right now that high end will not make up even close to 30% of your total sales. Out of 60 boxes I would say no more than 6-8 should be high end.
Keep in mind that if you end up selling a ton of high end cigars you can always skew the numbers that way later as you sell low/mid boxes. It's a lot harder to do the opposite...
Edit:
I would say low end would sell for 3-5 dollars, mid would be 6-9 dollars and high would be 10+ if you want a dollar range. The vast majority of what you stock should fall into the mid range, even your high end should be mostly on the low side. Not many people are going to buy homebrew and then grab a $15-20 cigar...