Dumpers refusing to dump on large ramp worksite

Issue description

In the attached save, I have a mining tower set to accept dirt, rocks, and slag to build a big ramp. For some reason I have a bunch of trucks loaded with dirt that are stuck doing nothing instead of dumping at the destination.

Expected behavior: trucks should dump to extend the ramp.

Reproduction steps

1. Load attached save. It should open to near a mining tower.
2. Observe that the mining tower is configured to accept dirt+rocks+slag and has a ramp fill project in its area.
3. Scroll down+left a bit (see attached screenshot to help find it).
4. Observe a glut of trucks in the mountain pass, mostly full of dirt, that are all in the "no valid place to dump" state.

Game version and build number

v0.6.4d (b343)

Operating system

Windows

Attachments

bugged.save

Add more designation tiles and wait. One is too small for the entire amount of dirt and slag.

When I do that, most of the trucks remain stuck. e.g. the truck in this screenshot, which is full of slag but not doing anything.

but sounds like maybe what's going on here is simply that the game only assigns enough trucks to unload to fill the accessible points on the ramp job? Which I guess isn't a straightforward "bug".

Maybe it would be an improvement if the game queued up all those trucks right next to the ramp and/or prioritized the closest truck to dump?

Thinking about this more: the present behavior isn't really a bug. It's just frustratingly suboptimal. So this is more of a feature request than a bug report.

bugged2.save