Some of these responses are just absurd. Like really really absurd. The combination of the point source speaker with the heavily radiused baffle are the main reasons that LS50 images so well. You're not hearing things. Your brain is not playing tricks on you. It has zero to do with the frequency response or any of the other other nonsense being touted and you're not wrong for preferring it. This isn't complicated.
Well, then it should be easy to prove you’re right. This is a science forum… all I see here (not just from you) is a bunch of speculation and arguments form personal experience and incredulity. This doesn’t really bring us near a solution and it’s not science.
Research says that preference scores for single speakers translate excellently to stereo setups.
So what is left are a few hypotheses that would actually be testable:
1. Placement of the speaker: height of the tweeter or toe in/out. this will influence both direct as well as reflected sound
2. Differences in on-axis (or listening axis), where the LS50 is the least linear of the two, results in the perceived difference.
3. The LS50 is a bit wider overall, creating the difference
Or combinations of these. #3 can be played with, like
@radix said. #2, can be experimented with using EQ. Make the response as close to the LS50 as you can. #1, is a matter of moving the speakers around a bit.
My uneducated guess is that hypothesis #2 will be the primary reason. Frequency response is simply the primary driver of how we perceive sound, and since radiation is still quite similar, my guess is that its influence is less in this case.
I for one, like the LS50 better when it’s EQ’ed a bit more linear (I like a bit more bass). In the end though, it may just be that you’re now very used to the LS50 sound. It's often hard to unlearn, and the question is if you should…? So if these things can help you bring back the old sound, plus some extras, go for it!