Need help with DCDigital/TV settings for Sega Bass Fishing “fish shadows”

[Avenger]

I am not very familiar with picture controls. I have a Dreamcast with DCDigital HW1 and a non HDR Samsung 4k TV. I ran into a problem with a particular use case. When you are about to cast a lure in Sega Bass Fishing, you see shadows of the fish in the water. I can see them somewhat in water that is bright but in darker light, the fish shadows really don’t show up. I am running in “force VGA mode” and 1080p on the DCDigital. On the TV, I fiddled with the contrast and brightness but can only increase the shadow visibility by a little bit. My TV doesn’t have a shadow detail setting but it has many others like gamma, black tone, etc, but it really didn’t make a big difference. Is there a TV setting I should focus on adjusting or maybe the DCDigital settings? Could thecDCDigital be negatively impacting the shadow visibility? I know this is a specific case where a shadow that is a few shades of color difference from the background needs to stand out.
I tried playing on an android handheld under flycast and the shadows stand out and look fine. I also tried connecting my Dreamcast to a computer monitor but had similar issues. Can you help?