The issue is not the space. The issue is the CPU and RAM limitation put onto the MSSQL Express instance by Microsoft, at some point your stored procedure might take too long which means tables don't get cleaned up as they should.
Seen that when customers had storage issues and some load was put on the SQL server by filling the events table quite fast.
As for the actual support statement, the installer now directly tells you the supported size of the environment with an express version of SQL which still is 5/50.