Responsive Visual inconsistency

I've been in the final stages of optimizing a website for a client, going through the multiple responsive states UPFRONT offers (which is really a cool feature btw, Love it ) and had everything just the way I wanted it. Tested it on several pc's of differing screen sizes, phones, tablets, etc. Everything looked good. My client looked at the website on her iPad Mini retina display and mentioned a bunch of inconsistencies, fonts were the wrong color, spacing was off on pages, etc. So I looked for myself on her iPad mini, lo and behold she was absolutely right.

SO - long story over, this website uses fixer, is there a way for me to add different responsive sizes to the responsive mode beyond the 3 that are offered? I notice spirit has 4 options.