The largest shot I have ever made successfully is sized about .110". This needs a set of drippers drilled about .040". The level of molten lead in the tray has to be as low as is practical . If there is too much flow the droplets run into one another and form mis-shapen blobs.
As regards the height of the lip from the coolant I have found the closer the better is the way to go . Raising the lip will result in molten droplets flattening and being less round , as will coolant overheating.
Coolants are a whole story in themselves. I have used diesel fuel with electrically powered shotmakers and it works well - cleanup being the problem . I have heard that near boiling water can be used but I could foresee a very nasty accident happening in my workshop .
Soapy water is another one I have not tried. My current coolant is a soluble machining oil "BP Fedaro M "mixed at about 20 to 1 with water. That is one litre of oil to twenty litres of water. I have been using the same batch of coolant for 15 years .It is stored in plastic drums under the bench and brought out as required. It does not appear to have deteriorated at all over the years.