I am running into issues with the Allow New Event on the calendar app. The required fields are set when you open details and you cannot make additional fields required. Other issues I find are fields that are included for display purposes that would normally be grayed out on an existing element (due to column formula) can cause the new event not to be created with no error if someone enters something in those fields then hit create. I can disable the Allow New Events but we migrated over from a share point calendar and our users are use to being able to create new items for the calendar without having to go to a different page.
My suggestion is if a web form link is added to the calendar that instead of new event button opening up details for a new event, it would instead display the form in the pop out.