If everything else fails, you could read the documentation, starting with man strip.
Seriously, maybe your application has a lot of symbols and code. At one extreme, the biggest size reduction would be rm elf but then your program won’t run anymore. It all depends on your program and what you coded into it.
As a concrete example, I recently worked with a large C++ library where strip without further arguments reduced the size from 400+mb to about 28 mb. But then you could not link anymore against it (in the context of other shared libraries), rendering it somewhat useless.
But when using strip --strip-unneeded, it changed the size from 400+ mb to 55 mb which is still considerable, yet allowed the library to be accessed from other shared libraries.
In short, I’d trust strip. Maybe your application cannot be reduced any further without code changes.