I'm trying to get a fillet along that edge that can blend into the larger radius but I'm absolutely stuck!
Try a variable fillet, example, you can do a .125r to zero,
I tried that but it gives a visible line that the light can catch.
can you post your 3D model here?
You can draw a closed profile in the corner and use delete & fill face to make all blend together
How about this?
I can't tell if it's the light but there is visible surface delineation?
Yes, it's then if you like it then you can use it to split the solid body
Ohhh. I see. Any chance you can reshare that part file? I'd like to follow your steps please.
Sure - see att. file
Then there is also this generally well-known method - Attached.
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