I reckon you could do the following to fix this issue: (1) add the barrier from option 2 to option 1, so that all the merging happens at the front. (2) Keep t

I reckon you could do the following to fix this issue: (1) add the barrier from option 2 to option 1, so that all the merging happens at the front. (2) Keep the "make both parties move structure" from option 1, but don't make it 100% symmetrical. Instead, nudge the top lane down just enough so they are forced to slow down and somewhat zipper in with the bottom lane.