Thanks to everyone for the assistance so far.
I can see I should have provided a few more details, so here goes. My Cornwalls, of which I am the original owner, are spaced 26 feet apart in a room 18x26 and they are in fact toed-in toward the listening position which is centered on the opposite wall. Only one speaker is actually in the bookcase, the other is on a stand in the corner of the room but will eventually be built in as well. The bookcase speaker is also in the corner of the listening room but, while the front of the speaker is flush with the bookcase, about 18 inches off the floor, the speaker itself is actually sitting on a shelf in a closet behind the bookcase, if that makes sense. This is where I'm wondering about building a kind of "false corner" surrounding the speaker.
The reason I think I can improve the acoustics is because I have experimented with placement of the other speaker by moving it out of the corner, getting it off the floor, etc, and saw a definite improvement in depth and width of the soundstage as well as improved bass and midrange.
And ,yeah, I know I should have a purpose-built, dedicated listening room, but,hey, you make do with what you've got. I'm in the middle of upgrading my sound system after nearly 30 years and have built new speker cables, interconnects, tube preamp and amps (was using a McIntosh MA6100 which is now my phono stage), new phono cartridge and SACD/DVDA player, and tweaking the speakers is my current focus. I may have to live with what I've got, which is by no means bad, but if I can coax a little bit more of that sweet sound out of my old boxes, so much the better.
Thanks again to everyone for replying.
Regards,
Gordon W