Hi Marco, for legacy code we originally started at “0% coverage on new code”. The 0% limit at least made developers consider tests for this old code even if its just a little bit.
Over time coverage improved and in tandem we have manually increased this check. In effect our % coverage on new code has increased in line with the % total coverage of all code.
Don’t expect it to change quickly, if you keep needing to make changes to the old code it will improve. If you don’t it will not change or you eventually replace that legacy code with something new which will have good coverage checks with sonar from the get go.