I never liked the look of the ETI box and made 2 of my own design but when I got my present one on the 21 for free because I was a returning customer I didn't turn it down.
One thing I never liked was the "falling forward" look. I understand that stemmed from the original box cover that was concave in the center and tilting it let it drain. That's not the case with the current design.
I got the box loose and mounted it myself. I used two wedges between it and the frame. Sorry, no access to the photos. The box stands upright with the lid level. The extra space I gained was enough to mount a second sewer type storage tube between the box and the shell.
Try undoing the box and standing it upright. It might solve your problem.
Ron