The aspects are what give you fragment slots, each aspect may have 3, 2, 1, or even no fragment slots. The amount of slots each aspect gives you is fixed, and there is no way to increase the number of slots available to you above and beyond what your two chosen aspects give you. So if you need more fragments you may have to choose different aspects, the ones that are weaker or more situational are the ones that have more slots than the aspects that have a more general effect or give a major advantage.