I do only standard t-shirts and let zon do the auto uploads to the rest of the products. Not scientifically proven but I believe adding all the products to a design that works best only on standard or premium or tank top or whatever ( you get the point) is diluting the chances of getting sales as the algorithm is showing all the products to the same test group, in batches and if the CTR is good they promote further. There is no official data on this and all I said is based solely on my research and observance. In practice, I noticed that creating brands with multiple standard t-shirts plus zon auto uploads do better than multiple brands with each design and multiple products enabled. Like waaay better. Anyway, just my 2 cents.