Stacking speakers can never sound good, and works against each speaker. It's a teenager thing to do, more noise and less hifi. It's not very clever.
Wel, it does have some precedence - solid reviews BITD of stacked Advent Lousdspeakers, stacked Quads in the HQD system, even some stacked Dahquist DQ10's and others. One could say that the early MTM D'appolito configuration arose from stacking speakers, then distilling them down to two mid woofers and only a single tweeter, of course with a crossover designed to work with that system.
The problem is the stacked systems even using similar or same speakers with original crossovers have many different interaction possibilities, plus the relative or perceived outputs of the drivers probably requiring L-pad adjustment, tweaking, or even redesign for the whole. And we're not yet getting into combing effects from driver spacing and imaging issues from multiple driver sources.
So it does open up a fairly large set of troubleshooting issues trying to dial in a stacked pair of speakers, if they can be. But it's harmless fun to try it out and see what happens, and then experiment with mods or treatments. The fun is trying things out, good or bad he/we learn something.
For example, one option here is to cut both the tweeters down by 1/2 volume each and then slowly bring each up to taste. Same for the mid control on the L36. I would also suggest inverting both sets of speakers to keep the woofers far apart and the mid/tweets closer together, the more classic way of stacking ( MTM configuration ). Also play them with grilles on as that cuts the HF a little.
Also, the right side speakers are in the corner close to the wall, so they will get a lot of boundary reinforcement of all the frequencies there. I would suggest as a temporary measure to hang a heavy fuzzy blanket on that side wall. Even when the speakers are run solo, that would be a benefit.