What determines the fitSharp runner Domain name?

Question

Why adding the ‘-a’ parameter (pointing to the TestLib.dll.config file) in the COMMAND_PATTERN, changes the AppDomain.CurrentDomain.FriendlyName value from Runner.exe to fitSharp.Machine?

Here are the root page variables I used:

!define TEST_SYSTEM {slim}
!define COMMAND_PATTERN {%m -r fitSharp.Slim.Service.Runner,E:\GIT\myapp\src\dotNet\_ThirdParty\FitNesse\release.2.2.net.35\fitSharp.dll -a E:\GIT\myapp\src\dotNet\Utilities\MyAppTestSuite\TestLib\bin\Debug\TestLib.dll.config %p}
!define TEST_RUNNER {E:\Git\myapp\src\dotNet\_ThirdParty\FitNesse\release.2.2.net.35\Runner.exe}
!define COLLAPSE_SETUP {true}
!define COLLAPSE_TEARDOWN {true}
!path E:\Git\myapp\src\dotNet\Utilities\MyAppTestSuite\TestLib\bin\Debug\TestLib.dll

I tried copying Runner.exe to where the TestLib.dll is located (and updating TEST_RUNNER appropriately) but that had no effect.