Git version: 2.13.0.windows.1
OS: Windows 7
CLI: Git bash
.gitconfig
The accepted answer, while helpful, does not answer the question.
As of this writing, includeIf only works inside a git initialized folder.
So if you cd into "~/Documents/webstorm/corporate/somegitproject" and run the command the output will be as expected:
$ cd ~/Documents/webstorm/corporate/somegitproject
$ git config user.email
corporate@email.com
This is probably a defect against git, since a user would expect this to work similarly in "~/Documents/webstorm/corporate/" as well.