MAF (maximum aerobic fuction) HR (heart rate) is NOT in your Z3. You should NOT be over that number (if you want to maximize aerobic function), it's not an average value for your run, it's the top limit, so your average HR for the run should be clearly below that number (obvious). You may walk in part of the route if it is too steep or you go longer than usual.
MAF is NOT Z3. I've not seen anywhere that.
"I considered..."
well, you (or I) could consider whatever zones :D
usually "zones" are 1 to 5, being 2 considered easy, conversational, nose breathing, ... pretty similar to MAF but not the same, being MAF more restrictive on the top limit. Do not cheat when calculating MAF, usually just 180-yourAge.