Sorry, there are no techniques that will guarantee setting pods on every try on diploids or tetraploids. The proportion of hand-pollinations that are successful will depend on the pod parent, the pollen parent, the temperature, the wind, the number of pods already set, the number of flowers yet to open, the humidity, the size of the fan/plant, the soil fertility and probably many more factors.
If you have a plant that does not set pods well in the sun but does in the shade it is probably temperature, humidity and/or wind that are the factors that are different and causing the difference in fertility (as long as the same pollen was used).
I have read the idea that setting pods on a tetraploid with diploid pollen will affect the tetraploid's ability to set pods later. I am very skeptical that there is any positive effect. A plant's goal is to set pods. Basically, once it has set some pods, the remainder of the flowers become less important. So, setting a pod, meaning the plant has now been successful and it must now use resources to develop the pod and its seeds, should cause the plant to be less likely to set later pods rather than more likely. I imagine any effect that is seen when this has been tried is caused by what appears to be a lower probability of setting pods on the first flowers that open rather than later flowers. If there is such an effect it could be caused by the weather. In any case the necessary test for the effect of diploid pollen on pod setting rates of a tetraploid requires that some flowers are pollinated by diploid pollen and on the same cultivar and the same day some flowers are pollinated by the tetraploid pollen in question. Then later the pod setting rates can be compared day to day. Since the weather changes from day to day and in a predictable manner (more or less) throughout the flowering season any comparison that does not check the effect of diploid pollinations versus tetraploid pollinations on the same days is not accounting for the effects of weather.
The pod of a daylily is like the fruit of other plants. The development of fruit is often affected by the development of the seeds inside the fruit. That is, the seeds produce compounds that affect the development of the fruit. Chambers that do not have seeds developing inside of them will not develop as well as chambers that have seeds. Pods with more seeds must become bigger, develop more, than pods with less seeds.
Most daylily hybridizers slather large amounts of pollen on the stigma when hand-pollinating, Presumably, if few seeds have developed then either most of the ovules had died or most of the pollen was not viable or most of the seeds started to develop but because of incompatibilities the embryos died and the developing seeds were aborted. In some cases it may be possible that the plant was not healthy enough to mature a full pod of seeds.
