Configurable parameters are way cheaper to fix *in the field* than a hardcoded value, even if they are undocumented and require reading the code to find. Set them to the sane default and ignore them until you need to repackaging, testing and deploying an application is EXPENSIVE.
Changing a configuration item in a backup environment and running a few sanity checks is relatively cheap in comparison.
If you aren't using a platform that makes configuration of everything that is not a nailed-to-the-floor constant simple then you should probably look into spending a few hours building yourself a small framework for doing so and reusing it on every project going forwards.
Even if it's just a simple key/value store added to your model and read out of your database at start-up and accessible anywhere in your application.