I think one of the reasons that there probably is no scientific study on the subject is that there are too many variables that contribute to the quality of a queen. I do not believe that any of those are the angle at which the egg was laid, nor do I believe that there are eggs that were destined from the beginning to be queens by some difference in the egg (the idea that the egg in a queen cell was any different than an egg in a worker cell was purported by Schirach and proven by Huber in the late 1700s.)

I think of all the factors involved, feeding is the biggest. It is related to the age of the larvae in that feeding of a worker or a queen is identical for some time, but changes somewhere in the first 36 hours or so and many suspect that some of those changes are less than 36 hours, if not in quantity, perhaps in quality. I try to graft when they are just a speck on a drop of royal jelly. Feeding has a lot to do with flows, how crowded the hive is with bees etc.

The next issue is how well they are mated. A queen that is poorly mated never does as well. The main issue here is plenty of mature drones flying and good flying weather.

The next issue, which is important, but I would put it after those other two, is genetics. You do need good genetics of bees that do well in your environment.

It is the combination of these issues that makes a good or poor queen.

Back to Jay Smith's observation. I think he is basing it on that time lag of when the larvae is not being fed because of the time to pull the frame, graft the larvae and get it back in the colony. With any graftless method the larvae is still in a pool of royal jelly while all this takes place which helps some. But the Chinese grafting tool tends to pick up that pool pretty well. Even doing the Better Queens method there is a time delay of cutting the combs and waxing them on and destroying the in between larvae to make room to separate the cells. All of this takes time. So I think we are back to them staying in that pool of jelly being the difference he is counting on.