Like GS fields indicated, the drone will break the height floor if it see that A the floor area is clear and it's other avoidance options are blocked which is typical in a forest. Don't count on that 8' being set in stone. I would also suggest when you're approaching a vehicle or person slow way down and approach carefully. If the drone hasn't cataloged the person or vehicle (circle around the person in the app screen) which is hasn't for people or vehicles that you are approaching so it wont see them and surprisingly will fly straight into a person, car or bicyclist. It's almost like a glitch in the OA but skydio warns about it in the manual. I didn't pay that much attention until the drone almost flew into my buddies head. He avoided the drone, it didn't avoid him. That's happened more then once and its rarely an issue with the height floor on except in scenarios like yours where there's obstacles that cause it to drop below the 8'.
BTW, you can loose the drone pretty easily on the moto, esp in the forest. The challenge as you'll discover is pacing your riding at or close to the drone's max speed for the environment which will be significantly slower around trees. Get it out in more open terrain and the pace picks up appreciably.