OK a lot of points there and good ones.
On my long rides I did use Vespa every 4 hours but one ride lost a packet so missed out !
Yes the training you mentioned is spot on, it is about training and not burning out that is Key to MAF.
As for HR because of Keto and what Peter Defty/Steve Phinney said then HR will be higher as fat oxidation uses more resources to get energy, remember carbs are quick and dirty and @Richard has mentioned this.
In training I do try and keep to the HR, check my rides out during this week for example, peaks will happen in cycling because unlike in running, walking up hills are not an option !!
However try and pick up Peter Defty’s interview with Brad Kearns on a Podcast - Primal endurance, that was so informative as Peter said in his view MAF HR can be up to 15 beats a minute higher.
On the big rides I ride deliberately at an higher HR as the aerobic base we have allows us to do that.