Speaker Placement Nirvana

My Spendor S8e speakers are on the short wall of a 15.5 x 18 room. The faces were about 4’ from the back wall, and about 5’ from the sides. I changed amps from a NuVista M3 to a Cary v12, and at 50W the Cary seemed like it was having trouble controlling the bass. It was a little boomy on some albums. After moving them around laterally, I decided to pull them further out from the back wall so the face is now about 5’ out. Wow. What difference that made. The boom is completely gone and everything sounds terrific. The change was NOT subtle. So my question is, what happened and why did the bass respond that way? I could see it if I’d had the speakers placed very close to the wall, but they were pretty far out to begin with. Any thoughts?
I do not know exactly what was happening - my guess is that @ 4' from the wall behind the speakers, speaker must have been in a peak node of a bass standing wave (all rooms have standing waves & their freq differs based on their/room dimensions) which caused that freq to be enhanced creating a boominess.
I *assumed* that your ceiling height is 8' & calculated the standing waves for your room. The axial modes are most powerful. Axial modes involve floor-ceiling, both long walls, both short walls i.e. any 2 parallel surfaces. I found that the floor-ceiling standing wave freq is 70.625Hz. Using speed of sound = 1130ft/sec, the wavelength of 70.625Hz is 16'. So, a quarter wave of 70.625Hz = 4'. So, if your speaker was 4' from the wall behind the speaker, you must/could have been at the peak of the 70.625Hz wave & that bass freq got enhanced creating the boominess.
Also, a tube amp, in general, does not have low enough output impedance (just the nature of tubes) to control the bass well to begin with. So, any room impairments could easily overwhelm such an amplifier.
You've just changed your Mustang for Schwinn. Certainly lower emission, healthier but substantially slower:-)

Room effects may somehow tweak this problem but not resolve. I believe the previous and further posters would agree.
I think Grimace has experienced what I have: changing the position of the speakers in the room absolutely swamps changes to electronics, cables, etc.

Marakanetz, I'm not sure I understand your comments. If you'd care to, perhaps you could be more direct in what you're saying. I'd be interested to know. It seems that Grimace did "resolve" his "problem." So I'm not sure what you meant. Thanks.
Mustang is Ford Mustang, a muscle car.
Schwinn is famous bicycle manufacturer.
I don't think that Grimace solved his problem since he does need current. Changing speaker position is only tweek(valuable I admit).
I'm not sure I'd equate the Cary to a Schwinn...
don't worry what he says
the Cary has low feedback which allows spendors to
project Strings voices and acoustic instruments in a very natural way.
Many a 1200 dollar amps may beat it in the bass but
grain out with the above by comparison playing a violin.
Try marking the top center of your speaker and taking it out from the wall in odd increments 1/3 1/5 1/7 1/9 into the room.
Measure the front wall of the room to the back wall in inches. then divide by 3 5 7 or 9 Place the speakers center mark on these grids with your preference on toe in.
Most odd increments should not disturb room nodes
Enjoy Cheers Johnnyr
"Mustang is Ford Mustang, a muscle car.
Schwinn is famous bicycle manufacturer."

Oh! Now I get it!

Of Course, that was the part I got, but since I didn't grasp the analogy to audio, thanks for the clarification.