SoapUI 5.2.0 doesn't start when incrementing Xmx to a value greater than 1280 in soapui.bat

How to resolve the following issue: The issue started because SoapUI 5.2.0 got frozen when running some scripts. Following recommendations, I increased the Xmx value in soapui.bat but noticed that if the value is higher than 1280, then SoapUI does not even start up. In my laptop I am running Windows 10  / RAM 24.9 GB / System type 64-bit.

Any help is appreciated.  Thank you.