I think it has to do with the fit except the person who is getting headaches I would go for a second opinion...

The basecurve on Freshlook is a 8.6 so sometimes the contact can feel to loose or to tight.

8.3 is way tight on my eyes for coloured contacts on normal contacts it is fine) and it feels like someone is squeezing my eye (Acuvue2 colour has a 8.3)

BASE CURVE (BC) has to do with the shape of your eye and almost everyone has the same BC for both eyes. Many contact lenses come in only one base curve, many others in only two base curves, some come in multiple base curves so care must be taken when ordering. If your box or prescription says MEDIAN instead of a number for base curve and unless we have the word "Median" as a choice "Median" is usually BC 8.5, 8.6 or 8.7.