bubble:
zScaling: Boolean
zScaling controls whether to draw the bubbles of different size (based on z value) or to draw same size bubbles (helpful in case your data-set contains values that extends to extreme ends)
minBubbleRadius: Number
Minimum radius size of a bubble. If a bubble value is too small to be displayed, this size will be used.
maxBubbleRadius: Number
Maximum radius size of a bubble. If a bubble value is too large to cover the chart, this size will be used.