when I load an event with a customised event notification pattern it does not appear on the guest calendar (it reverts to their default setting). How do I ensure the guest receives the same event notifications I do as the event organiser?
You cannot. Google simply has not enabled this as a feature of Calendar. Calendar reminders and notifications are only alterable as per-account settings. My personal guess is that they felt it would be too easy to abuse, whether inadvertently or intentionally. Google is a hulking corporate giant, but they do say they still welcome feedback. If you choose, you can always select Report a Problem from most of their products' Help menus and explain it to them.
If trying to accommodate travel time, event preparation, or other timely considerations, perhaps consider the workaround I've seen in use most often; treat your multiple-notification need as multiple events. E.g. most invitees just get the meeting invitation, naturally with their own notification settings, but you also send a second, "travel time" invite to the field office's attendees, scheduled some appropriate time in advance.