Okay you want positioning tweaks? We got positioning tweaks!
Start by tweaking the speakers to precisely the same distance and angle. Precisely means within 1/16". This is easiest with a range-finding laser-level. Aim the inside of each speaker to a point a few inches to the outside of each ear. Otherwise, old-school line and tape and framing square works fine too. The way you measured the sides to the wall is fine, just do that across to the other speaker to make sure both are aimed the same and perfectly symmetrical.
While you're at it make sure they are perfectly square/vertical. Its easy especially with carpet and spikes to have them leaning a bit. So even if you get the distance right the dispersion will be off.
Now once you've established this have a listen. Even a small tweak should have improved imaging. Now try tweaking toe-in just a bit. Pointed right at each ear imaging will be incredible. Toe'd out a little won't lose much solidity but will tend to improve a sense of space. Toe out too much and the sound will be wide but diffuse. Tweak small amounts and listen.
Now you have the challenge of a wall on one side, open space on the other. There's this thing with humans, sounds that arrive within about 6 milliseconds tend to be perceived the same. Sound travels roughly 1 ft per millisecond. So your goal is to have the first reflection sound path at least 6 feet longer than the direct path measured to the speaker. You can measure to be sure but at 40" I think your left speaker is a little too close. Experiment a little. You may find it works better to shift both speakers just a few degrees to the right. Either sideways, or rotating to the right (as seen from the sweet spot). Experiment! Nothing, but nothing, beats tweaking speaker placement in terms of cost/benefit.
From there you might want to try moving them a little closer. Maintaining the same angles this will bring them further from the front wall and the left one further from the problematic window. Should improve imaging even more.
Won't take much of this to develop a pretty good sense of what works for imaging. With a feel for that you can then work on getting the best tradeoff between imaging and frequency response. Sitting so close to the back wall is an even bigger factor than speaker placement. You may notice moving even a few inches closer or further from the wall changes bass response a lot.
There's no right answer, its all trade-offs, but you got to put in the work to get a feel for what those trade-offs are. Its never perfect but you may be surprised just how much better it can be with a little work.
Start by tweaking the speakers to precisely the same distance and angle. Precisely means within 1/16". This is easiest with a range-finding laser-level. Aim the inside of each speaker to a point a few inches to the outside of each ear. Otherwise, old-school line and tape and framing square works fine too. The way you measured the sides to the wall is fine, just do that across to the other speaker to make sure both are aimed the same and perfectly symmetrical.
While you're at it make sure they are perfectly square/vertical. Its easy especially with carpet and spikes to have them leaning a bit. So even if you get the distance right the dispersion will be off.
Now once you've established this have a listen. Even a small tweak should have improved imaging. Now try tweaking toe-in just a bit. Pointed right at each ear imaging will be incredible. Toe'd out a little won't lose much solidity but will tend to improve a sense of space. Toe out too much and the sound will be wide but diffuse. Tweak small amounts and listen.
Now you have the challenge of a wall on one side, open space on the other. There's this thing with humans, sounds that arrive within about 6 milliseconds tend to be perceived the same. Sound travels roughly 1 ft per millisecond. So your goal is to have the first reflection sound path at least 6 feet longer than the direct path measured to the speaker. You can measure to be sure but at 40" I think your left speaker is a little too close. Experiment a little. You may find it works better to shift both speakers just a few degrees to the right. Either sideways, or rotating to the right (as seen from the sweet spot). Experiment! Nothing, but nothing, beats tweaking speaker placement in terms of cost/benefit.
From there you might want to try moving them a little closer. Maintaining the same angles this will bring them further from the front wall and the left one further from the problematic window. Should improve imaging even more.
Won't take much of this to develop a pretty good sense of what works for imaging. With a feel for that you can then work on getting the best tradeoff between imaging and frequency response. Sitting so close to the back wall is an even bigger factor than speaker placement. You may notice moving even a few inches closer or further from the wall changes bass response a lot.
There's no right answer, its all trade-offs, but you got to put in the work to get a feel for what those trade-offs are. Its never perfect but you may be surprised just how much better it can be with a little work.