Speaker Cable Malarkey (“Ghost” Cables)

I have an interesting phenomena on my hands. I recently ran 15’ runs of 12 gauge and 14 gauge to my mids and tweeters, respectively. Coming from much smaller gauge wire for my tweeters (and shorter runs) of 23 gauge wire, I noticed a significant change in the highs - they were more tamed and subdued. The mids were less dynamic too.

My solution was to run more cables in a shotgun configuration - another 12 gauge to the mids and a 20 gauge to the tweeters. After I hooked it all up I felt that the highs were harsh and brittle which may have been from a lack of cable break-in. In any case, I disconnected the 20 gauge at the speaker and left the other end attached to the amp because it is hard to access and I just wanted to see what “removing” the 20 gauge would sound like for the time being.

Here’s the thing, the treble was tamed a little bit but no where near just the 14 gauge alone as before. The 20 gauge wire isn’t connected to the speaker terminals but it’s still being energized by the amp and it is somehow altering the sound like it is connected.

What is going on here?