improve support for short trains in long stations

So long trains in short station support is great... After filling the first cars, the train works it's way forward to fill later cars. However, support for shorter trains in longer stations (4 wagon train in an 8 module station) isn't anywhere near as good. The 4 wagon train will always stop at the first four modules and will only attempt to unload there. I've run into the problem a few times now when switching from shorter trains and stations to longer trains and stations where a longer station ends up being starved because shorter trains keep trying to service it and only the first four modules end up being serviced.
As a recommendation either a sliding unload like we have for load, or run a calculation for every fitment (1-4, 2-5, 3-6, etc) stopping when you hit the first full unload, and if you make it all the way through, using the fitment that gives the highest unload.

Maybe too complicated, is there a reason for stations that big? If you need more storage room, just build storage after those modules, that way it will not matter you are unloading to less unloaders.

This happens when transitioning from 4 wagon trains / 4 building stations to 8 wagon trains and stations. The 8 wagon trains can be serviced by the 4 module stations just fine, although they can block traffic while doing so (other stations in the same loop, like a mine). But a 4 wagon trail will only ever service the rearmost 4 modules in an 8 module station, even if those modules are all full.
I was attempting to avoid having to split each line into two, one where delivery stations are only 4 modules vs when delivery stations are 8. An 8 module station isn't that big, and yes, I do use output buffer storages as well.