Sonos Arc poor dialogue, echoey, Atmos not detectable in small room?

I got a Sonos Arc SL and two One SLs for surround sound refurbished from Sonos' website. I'm really impressed with them in many ways but dialogue, which I think is the most important thing, is not amazing. Now it could be that better audio equipment exposes poor quality audio more but specifically with dialogue I find that it can be veiled/tin can-y, less clear than I would like, and recessed to the point of being hard to hear in loud scenes sometimes (which is supposed to be the whole point of a center channel but there's no independent volume control and my Audioengine HD3 PC speakers seem to give clearer and more natural dialogue than this does). Several of the options in the app seem to have little or no difference, including Dialogue Enhancement. I've found even in the highest-end audio, making music and sound effects sound great and envelope you around the room is easy, but making dialogue sound natural is the hard part.

I did the Trueplay (or rather my friend did, spinning his arm in circles all over the room). I heard that adding a sub improves the mids and highs on the soundbar, so I bought a new Sub Mini, but flipping the switch on and off shows no difference besides a booming low end in very bass-heavy scenes and music (and no rumbling of the room, which I guess is by design given the force cancelling design).

Additionally, some dialogue sounds echoey, and I really can't detect overhead sounds, though I thought this might end up being the case going in as I'm in a small room (about 10 feet wide), so I'm sitting about 6 feet away from the soundbar. The TV and soundbar are both on a stand with the soundbar several inches in front of the TV.

So I guess I'm wondering if this is normal for the Arc, if it's normal for soundbars in general, if there's anything I can do about it, etc.