Binding posts tightening physics and drastic change

Hello to you guys. I just do not get it from scientific point of view. Here’s the case. As a Hi Fi man since many years I came to buy a pair of great monitor ( passive ) speakers ( the company has in this case nothing to do I guess but this is a second pair of the same speakers I had before ) I just happened to spend hours and hours to get the right position and sound ( as all monitors are very susceptible to set ups and so on ) and now this - as a purist I always tighten but not overtighten binding posts with banana connectors - yesterday I do not know why I made loose a bit all the screws on 4 binding posts so that they are not so strongly tightened up - and now the sound finally came to life and sounds much better with a bit more bass - I am no kidding in this case as I am an analytical listener. Please explain what the hell ? Almost anyone says that tightening should improve the sound - here it is quite opposite. Regards.
P.S. The more to add that there are no cable jumpers but metal (copper) links.