I am specifically talking about when the unit ends its turn on the goal tile. When moving at a great distance your army will end up on each others tiles unless your army is small,its completely flat with no hills/mountains, or all of your units have exactly the same movement points.
To get back on topic, your original question was:
The answer was that people hate micromanaging the movement of armies to the battlefield. You might not have that problem, but plenty of others do. I and many others (I think, obviously can't claim to represent everyone) don't find micromanaging movement in battles annoying. Its the mass transportation of units thats annoying. Same with moving large amounts of units across the sea.
To get back,back on topic. The marginally decreasing strength per tile is still pretty overpowered. 4 swordsman would have an outsized advantage over 1 swordsman oneshotting it, forcing most swordsman to group together. I think you've misjudged your formula because the strength value in the first place is already logarithmic? or something like that. So adding strength by a percentage of the original would actually preserve 2 swordsman strength in one tile.
Practically speaking it would shift 1UPT to like 3ish UPT. Besides how would a 3 swordsman lose to anything else in the era? The only way is to get 4! swordsman. [correct me if wrong]
I think there should be multiple units per tile at fixed number. idk 6 or something. And only allow 1 attack per tile. Damage inflicted on the one unit on the tile will affect all units on the tile at a lower rate. Or something like that. idk how to create balanced stuff.