I'm on the team here at ZingChart. There is an attribute you can use to adjust the bubble radius that is not dependent on "scale-y":{}. Here is some code that will be helpful.
{
"type":"bubble",
"plot":{
"max-size":200 */the "max-size": attribute accepts numeric values and will adjust the radius of the bubbles independently from the y axis values/*
},
"scale-y":{
"values":"0:20:5",
},
"series":[
{
"values":[[1,15,4],
[2,4,2],
[5,10,1],
[6,7,3],
[3,6,2],
[7,15,1],
[8,2,4],
[1,7,3],
[2,12,3],
[4,4,4],
[5,1,2],
[6,3,1],
[8,16,2]]
},
{
"values":[[3,5,1],
[2,17,2],
[8,8,3],
[4,6,2],
[7,3,4],
[2,12,1],
[1,4,1],
[6,2,2],
[4,10,3],
[6,14,2],
[2,6,2]]
},
{
"values":[[3,11,4],
[6,7,4],
[8,14,3],
[3,2,3],
[5,5,2],
[7,10,2],
[2,1,1],
[7,4,1],
[6,16,2],
[1,8,3],
[5,14,1]]
}
]
}