Ah, but that presupposes a rectangular area.
Let's say our user "JONES", has, just like a beagle with his nose to the ground, swept up many tiles at highest resolution along his section of Highway 8
(We note HY 8 is not exactly east-west, nor north-south.)
That was last week and he has now intensely edited OSM and would like to refresh large portions of those tiles.
All he wants to do is sweep up new tiles, just like he did in the first place.
As the standard expiry period has not elapsed, sweeping again will get him nothing.
If he used the rectangle refresh approach it would take hours, and fill his cell phone up with useless high resolution tiles of irrelevant mountains.
Therefore what is simply needed is perhaps a small "Refresh mode" icon. (Perhaps just use the standard looped arrow, as seen in browsers' refresh button: U+21BB CLOCKWISE OPEN CIRCLE ARROW "↻" )
Have it somewhere near the edge of the screen, when in online mode. Or deep in the menus, OK too.
When the user taps it, it becomes red and pulsating, meaning "activated".
The user can then simply sweep along the road like he originally did, vacuuming up fresh tiles from the server.
When he is finished he taps it again, deactivating it.
Or if he forgets, I suppose you can deactivate it when closing the app...
Anyway, as you can see this would be very easy to implement probably.