I figured it out! I was right, the dimensions need to be the exact or otherwise it will add a white background to the image. I also had to change my image dimensions from inches to pixels Thanks again.
Thanks for the tips. We might have different versions of macOS, but I sort of figured it out. I downloaded the picture and opened it via Preview. I cropped the photo just as you said. My problem is dimensions. If I recall correctly, if your image is bigger than the avatar dimensions (125x125) then it will add a white background to the image. However, if I try these dimensions in Preview, it's very very small. I think I need to play with it more, but I feel like I'm in the right direction.
I want to use the Riku render (and do a close up like you) but I've been out of touch with photo editing software. Any chance you could help? It's funny, ages ago I posted a thread on how to do it, but I've lost my ways after switching to macOS. Tips would be helpful too.