Then it struck me that Darkwater Crossing is exactly AT another border, namely the border between Eastmarch - ruled by Ulfric - and theRift. Makes much more sense if it's that border Ralof meant. What do the rest of you think?
Lokir says "if it hadnt been for you stormcloaks I'd be halfway to Hammerfell by now" or something like that. Impling to me a means of distance rather than a destination.
The op's point is interesting though, but as said it would be strange to set up an ambush between 2 stormcloak held territories. I think the more interesting point is how did Ulfric allow an ambush in his home territory. Laziness it seems to me.