First, let me thank you for taking the time to read through the rules and comment them!
Regarding the distance travelled, I've prefered to stick to what the rulebook says. I'm no expert at hicking and don't have a personal criteria to adjust that. Also, I prefer to make calculations easier and faster than to be absolutely true to reality. To me, the main goal of the rules is to simulate the fatigue and hardness of journeying through Davokar, not to calculate the exact amount of time it woud take in real life; that is, I'm more than willing to sacrifice realism if that helps us to focus in the hazards of the travel, by avoiding long calculations. As the map I use is divided in hexes that represent 20km, then that speed makes everything smoother.
That said, I've also read many arguments saying that it's not the same to calculate the distance a modern person can walk by foot, with perfectly fit and designed backpacks, training in hicking, no weapons or armours or loads of treasure and not needing to beware of their surroundings out of fear for barbarian attacks, etc. A usual group of adventurer's might also include a weak loremaster that doesn't endure much more than a few hours of walk without falling to the ground, rations are scarce and need to be replenished, paths aren't marked, etc.
But mainly, my take on this is to make the rules calculations as smooth and fast as possible. Of course, if you'd like to change that, I don't think the rules would "suffer" from it, as the number of Hazards found during a journey depend on the number of days passed in Davokar, not in the distance travelled. In very long journeys, there might be a difference of one or two less hazards overall. But I don't think that should be very significant.