More chance of the joist catching fire than the insulation, that's why they're separated. That's the key element here, the joists, literally don't worry about the fibreglass. Infact insulation is incredibly difficult to burn, it just melts, even at ridiculously hot temperatures.
Fire rated lights with LED lamps - i'd be able to fit them nearer a joist than manufactures recommendations and sleep easy at night. These are just recommendations, and yes if anything went wrong you'd be bent over a caldron, but, the office boys that right these recommendations don't live in the real world, and occasionally, your professional judgement will override.