Would you consider the Mopar Suspension Manual a proper reference? It's all right in there under the leaf spring rear suspension section. Read it. It talks all about the different rates between the front and rear segments, talks about how important it is not to over torque the U bolts. What?!?! Different rates for front and rear segments on the same spring? Guess what? That can only mean one thing. That the front and rear segments move independently of each other, just like I described. It even references the "booming" sound it can cause when they are over torqued. With the SS springs, it's more than just the sound. It can make for a harsh ride as well. It's all in the book.
Look guys, this stuff has been around since the beginning of leaf spring suspensions. What? On horse drawn buckboards? Before that? Question me all you wish. But this information is certainly nothing new and it's correct. I haven't dicked around the better part of my life as an alignment/suspension mechanic to learn nothing.
Now, what do you want next? A page number? Ok. Mopar Suspension Manual 9th edition. Start on page 307 at LEAF SPRING REAR SUSPENSION and go to page 316 all the way to the bottom. That way, you'll see it all , instead of one or two points. In fact, finish the whole section. I recommend it.
When I am adamant about something, it's because I am damn right about it. I don't really give a fig what you "doubt", "don't believe" or "think is wrong". It's not up to me to lead you by the hand and educate you. You wanna keep arguing? Go ahead. On this, you'll just be wrong.