Calendar - macOS vs iOS

When I create an event on a Macintosh (MacBook, 10.14.6 Mojave) with 30 minutes travel time and set an alert for 30 minutes before travel time, it almost always appears on iOS devices (iPad Air 2, 12.4.1, for one) with 30 minutes travel time and an alert 60 minutes before travel time. On the iPad, all default alert times and Time to Leave are turned off. Any ideas what setting I need to tweak to get the iOS devices to use the alert time that I set with the event when I created it on the Mac? Thanks.