No, You cant,But i have other way to achieve this issue.
1.Create a Dual Axis like below.
Make sure, you have one is Line and other is Circle and Apply Dual Axis.
Once you have dual axis, then you can increase size in Circle Chat mention above. Attached workbook for your reference.
10-25-2018.twbx 8.5 MB
Thanks Venkatram, this is a nice work around
I was also stuck at another problem - let me know if you can help:
https://community.tableau.com/ideas/1500 ->pls scroll till the end for my post