Yes, it looks like these values are hard coded in the plugin. I'll create a defect ticket to get it corrected. In the meantime, if you have appropriate permissions, you can hand edit the plugin to correct this yourself.
Navigate to the plugin: Automations> Administration> Plugins > EC-EC2
Navigate to the procedure: API_RunInstances
Edit the Custom Procedure Property, ec_parameterForm
<propertyType><instanceType>, you will find option blocks like:
You can add or remove these as you like.