D750 + EFH + Raleno Light Leak Questions

I’m scanning negs for the first time, my setup is

Nikon D750 + 55mm 3.5 micro + extension tube
Raleno led panel
Essential film holder

I seem to always get excess light coming in, usually on one side, no matter what I do. It’s more severe in 35mm for some reason but I still get it in my 120 scans. In the 120 shot just compare the left side to the right on the floor and you’ll see, in the 35mm scan it’s on the left and parts of the right too. I’ve tried to block off as much light as possible with no real difference, it could be excess light coming through the space between the frames but I’m not entirely sure. It doesn’t seem consistent with the lens vignetting though so I don’t think it’s that.

Any help appreciated, thanks!

Did you take the shots in complete darkness?

Blocking light from shining in between the negative and the lens can make a difference.

I did, yes
Not sure how I’d block light between the negative and the lens though, I even used a small tube to block ANY light coming in externally to no avail so unless the light is literally reflecting off the lens and going back onto the negative, I’m not sure what I can do.
Maybe because it’s a 55mm and it’s quite close to the negative?

This is a possibility you can easily eliminate if you take a few test shots from farther away and at an angle. Using a polarizer can help reduce reflections.

Also move your light away from the negative. Edges of negative holders can add some stray light too.