FRatSTN
Basically the AMS frequencies are reduced in the summer months to accommodate additional 'sun' flights so 2016 is no different to this year in that regard.
There is indeed a gap of about 4hrs50min at 12:30 on Monday, Wednesday, Friday and Sunday so certainly room for a relatively close destination to be added, although I cannot really see IOM or CDG being that destination. That is the only unused slot in the programme so a fourth aircraft would be needed (or a w-pattern on a non-based aircraft) before additional destinations could be added.