To adjust the bubbles of multiple charts to the same relative size you currently need to use the following work-around:
- Make sure that all concerned charts have the same design and size. If, for example, one chart has axis labels and the other doesn't, the bubble sizes might differ slightly.
- Choose a bubble size that is larger or equal to the maximum size of all bubbles in the concerned charts. Put this value as an extra row into the datasheets of all concerned charts.