First off welcome to the forum!
That's a really good question not just for folks that trailer but also for those that carry heavy loads in the bed.
To be honest I haven't towed with my STA once since I have owned it but I did load it up a couple times well beyond capacity. I am sure I had it loaded well beyond the tongue weight of anything you would tow with your STA.
I am the type that likes a visual aid so I went out this morning and tried to capture some pics. It was difficult crawling under and getting a decent picture.
It was really cramped and I really couldn't get the angle I wanted no matter how I tried.
My thoughts on your question are this.
There is approximately 2-1/2" inches from the top of the half shaft to the top opening in the frame.
From the bottom of the half shaft to the bottom opening of the frame it is approximately 2".
My measurements may be off a little but I am confident they are close.
For the sake of argument let's use 2" as the drop.
So in theory with the new Spring installed it is shortening the gap from the top of the half shaft to the top opening in the frame to 1/2" of clearance.
When carrying or towing a load you are weighing down the entire rear, IR included, compressing the springs and changing the angle of the half shaft to the wheel possibly bringing it closer to the top opening of the frame.
So in answer to your question, yes I think it could be possible for the half shaft to rub the frame if the vehicle is
over loaded but again, as you folks know, I am not an expert.
I am hoping someone with more knowledge on the subject will chime in with their thoughts.