The hauling system overall is pretty frustrating >:( at times in this amazing game!
The primary concept of my suggestion is already a mechanic present in the game...
If you want to make a "bill" at you production tables (for instance in the butchering table), you can see there is already a range that varies between 0 to 999 (no idea the measurement). The fact is that you can reduce or expand the radius of search and make your production way faster. With this simple change you can have individual stocking piles that do not intervene with each other.
My other suggestion, and actually my better suggestion I think, is introducing specific routes for every single stocking and dumping piles in case you need to. You need to draw the path and finally get your people get all those nasty chunks out of your base. It might be even better if you could mark a zone with items you want to collect and create a bill, for example marking an specific area. This could work with the way the game already works with bills, so you don't have to micromanage every single piece of chunk out of your base and you could have many single dropping/dumping piles without interfering with each other. When there are no more of the looked items you are looking for inside the designated area, the bill will be marked as completed (a notification should be showed, same as with all the bills in the game), unless you have configured this to be "do[ne]for ever."
So here, those were my five cents on that matter.... this could obviously work much better if we could have backpacks and carts/vehicles which are an absolute necessity in the game as it is right now.
Hope these can make it to the game...
;)
Pathfinding tends to try and find the fastest route between two points based on walk speed over various types of terrain (not necessarily the most direct one.) It's not super-smart past a certain radius, but within 100 tiles or so, it seems to work pretty well overall.
IMO, your best bet is to lay down concrete paths between different parts of your map. Your pawns will tend to stick to those walkways, because their movement speed is 100% over that terrain.