There are too many factors that you can't control. Only way is years and years of experience trying different methods. Comes down to thorough but light see to soil contact. Too much direct and the seed won't grow either. Hardest thing is control the watering.....when I did it professionally each customer was required to use one of my sprinkler timers. I would have it come on 3 times a day with a impact rotary sprinkler 20-30 after the 1st thorough ground soaking. You want the ground damp inbetween waterings but not so much it doesn't dry out or almost dry out before the next one. You do this for 5-7 days and then start backing it way off. If you do this the results are amazing. We did this and guaranteed our results. The owner was responsible for watering the rest of the property like we showed them. They could do it manually or with timers.