Yes, there's really not much to go on in terms of finds. There are only a few depictions. The picture in the original post is from the Aemilius monument constructed after the Battle of Pydna in 167 BC. There are a few other depictions, as well. I think LL is very close to what is typically shown in the few reliefs we have.

I don't really like to compare to DeI. That's a pretty high bar to clear. They are currently using the shields Kaziel's excellent Roman overhaul, if I'm not mistaken. Many mods (to include our own) have borrowed heavily from his work. In terms of the shape of the shield, though, I do think LL has hit it on the head here. Kaziel was working on a new one of his own, but unfortunately it hasn't been released yet. I love what LL has done here with Solitudo's model.