Hi Ammar! As far as I can tell, Tableau is automatically shrinking the circles based on the width of the columns (which are being adjusted by the fitting mode). I don't know if there's a way to completely stop Tableau from doing this, but you can try shrinking the default size of the circles to try to avoid it.
Thanks for your reply.
Shrinking the default size is not working too, whatever size i choose for the circle will make it change when data points change.
Could you create a parameter, and then set the size of the circles to that?