Well the Duco cement Ive been using is a one part type, so I think I was wrong to call it an epoxy. I think it would be better classified as a glue.
I have tried larger drops to make a bigger lens, but the same problem the glue seems to shrink as it dries and deforms the initial smooth surface. The temporary solution to that was the blow a bubble under it. But I think a true fix would be to find a right material such as a more viscus super glue, or other type of clear drying glue which does not shrink on drying and is not runny. The bubble lenses would create 4 surfaces where light passes through as opposed to 2 if it were a solid lens which probably would be better.
I will try out some of your tricks, maybe coat a sheet of plastic in spray on oil and try to create ones on that, as well as widening the hole when I get a bit more time hopefully this weekend.
I have been thinking about trying to dry them suspended on a bit of floss, such as when water is suspended on a spiders web. But that might get a bit messy, and the shape maybe less spherical when moving to a larger scale.