Blend Modes - What am I missing?

I have a pretty good understanding of photoshop blend modes and I’ve looked at the the various posts and tutorials I can find, but blend modes still seem to do something different than I intend.

(Sorry - I had images for all of these, but new users can only insert one image.)

If I want to set up a bunch of videos in a grid (like a Zoom meeting or virtual choir), I would think that the default “over” setting should work, but all I get is that layer and the one above it. Nothing below it.

I don’t understand why all of the layers are not visible if the blend is set to “over.”

Using “none,” I only get that layer. Nothing above or below.

Using “add” gets this:

The only way I could make this work was using the “add” blend mode and a crop filter on EVERY clip. This seems like a good workaround, but I don’t think it’s the way it’s supposed to work.

What am I missing?

Somewhat related to this problem: This is anecdotal and I can’t replicate it every time, but sometimes I’ll make a change to one of the lower layers (make it visible or add a filter) and everything above will suddenly appear on all layers. I’m usually so surprised when that happens that I don’t take note of what I just did.

While I was totally stuck with this problem yesterday, I think I figured it out. I wasn’t finding the answers I needed because I was looking for help with blend modes. The problem was actually with the cropping filter. I found the answer here:
https://forum.shotcut.org/t/cropped-videos-wont-overlay/11691

Basically, if you crop videos for an overlay, the padding alpha channel has to be set to 0.