Does anyone have any experience/knowledge with mourning dove nesting behavior?

The top left platform was used continually during the nesting season the previous two years after I built it. I think I had 4 successive pairs of fledglings each summer.

At the beginning of this season, in may, the first fledgings were taken by crows. I have a backyard security camera that I was able to watch the action. The nest sits on a beam beneath my pergola and there's not enough vertical space for a crow to land, but one managed to figure how to basically fall from above and land sideways and get his head in there to grab a baby dove before completely falling down.

The nest has been scoped out by crows before but this was the first time one was taken.

So I built the lower right one, which puts the nesting area about six inches back, hoping it will be enough that the crows won't be able to get them. But it hasn't been used at all this season. Doves will occasionally check it out for a few days in a row. One pair even began building a nest but then abandoned it.

Also not shown is a small roof above the pergola I built to protect the nest from rain. I also made it a tiny bit bigger as the mentioned Crow was trying to get his face between the pergola slats but couldn't reach the squabs. I'm also hoping this slightly bigger roof makes the platform more hidden from predators.

I don't really want to reduce the size of the roof because of the crow issue.

So why was the slightly smaller platform so successful, and this one isn't? Any strategies for attracting doves to nest?