Maturity, in terms of both age and size, is a huge factor. Pre-breeding condition, the cycling process, and maternal temperature are other key ingredients to viable clutches. (the maternal temps I am speaking of are post-ferilization, and pertain more to egg viability). If you are sure that both the male and female are mature enough, I suggest looking at condition and cycling. Before I go any further, I will state that I have never bred retics...but I have encountered similar results with other species. Don't over feed the male. keep the female on a regular feeding schedule for most of the year, then increase her feedings (either frequency or size of meals)...I know I won't explain it correctly, but it has to do with body fat and egg production (or something similar...I recently saw an article that explained the science of it pretty well. I'll see if I can find it again). With some species, the cycling temps and the timing of introduction can be major factors in the success of the breeding. Again, not having direct experience with breeding retics, I will only mention the subject and let those in the know speak to its applicability (and the details, if appropriate). Feeding during/after the breeding process...hmmm...When I bred burms, I stopped feeding 3 weeks prior to cycling, and never fed them again til they laid eggs. I had great results with this, but it depends on the body weight of the snake. working with smaller, leaner snakes now, I feel that they do better with regularly offered (if slightly smaller than normal) meals. this also decreases the physical toll of parturition (whether egg laying or live birth), and allows them to get back to normal condition faster and easier.
Good luck, Art