The zones should be treated as a guide only - we are all unique and the general guidelines you see for heart rate zones out there are just that - general and guidelines.
If you read anywhere that you must stay at an exact heart rate or an exact heart rate intensity then take that advice with a big grain of salt and modify it based on all the other signs your body is giving you.
Your aerobic zone might be anywhere from 65-80% , threshold anywhere from 80-95% and VO2 anywhere from 90 -100 %.
Re running hills , average heart rate isn't the main thing. You could go way over your aerobic zone going uphill and then way under going down but averages out in the zone. What you have effectively done is a tempo session and a long warm down. That's not an aerobic session just because the average is in your aerobic zone .
Heart rate is to the be all and end all of training intensity , its a guide and should be used as just that unless you have a LOT of experience and are running a flat course.
So if you want to do an aerobic run , when you get to a hill , if its any more that a very short one slow down , to a walk if you have to because if you don't you aren't training your aerobic system .
Each run should have a purpose , if the purpose is to develop aerobic fitness then you should stay aerobic .