Create an alias for a SQL Server named instance pointing to sql default instance
My observation is it is necessary to use cliconfg.exe on the application server in order for it to map a specific instance (e.g. '\crazyapp') to the default instance on the remote SQL server.  

On the application server, I have set aliases using cliconfg.exe, using both:


C:\Windows\System32\cliconfg.exe (64bit) and 
C:\Windows\SysWOW64\cliconfg.exe (32bit)  (thanks, @DaniSQL)


From the application server, I have configured:


I then successfully tested this from the application server, using SSMS to the remote SQL instance.

Creating the alias on the server hosting SQL Server does not work, even if the application server can resolve the SQL Server name via DNS. In order to map from a named instance to a default instance, the alias must be created on the application server.

Thanks to @ypercube for guiding me in the right direction.