Japanese Cotton Sponge Cake - How to stop collapsing?

I've recently found videos about Japanese "Cotton" Sponge Cake. (Possibly also called a 'Jiggly Cake'?) I've never had it, but I figured it looked good, so why not try it? All of the videos I have seen list ingredients, and demonstrate technique, but don't necessarily explain the techniques. I feel I have missed something. In particular, 2 of my 3 sponges collapsed very shortly after they come out of the oven. My three variations all used the same recipe, but had varied baking technique. Here's the recipe I've been using:

Ingredients:

• 50 mL canola oil
• 80 g cake flour
• 1/4 tsp salt
• 1/4 tsp baking soda
• 90 mL half and half *
• 1 tsp vanilla extract
• 1 egg
• 5 egg yolks
• 5 egg whites
• 1/2 tsp cream of tartar
• 80 g sugar

Method:

• Preheat oven to 350 F.
• Heat canola oil in a pan. **
• Whisk together flour, salt, and baking soda in a medium pan.
• Add the oil to the flour mixture and stir until smooth.
• Add the half and half and vanilla to the mixture and stir until smooth.
• Add the egg and egg yolks to the mixture and stir until smooth.
• Add the egg whites and cream of tartar to the bowl of a stand mixer, stir.
• Whip the egg whites until foamy.
• Slowly add the sugar while continuing to whip.
• Whip to medium to stiff peaks (under is better than over).
• Add 1/3 of the whites to the flour mixture and incorporate.
• Switch to a spatula. Add the remaining whites to the mixtures in two batches, folding gently to just incorporate.
• Gently pour the mixture into an angel food cake pan, smoothing the top.
• Bake for 50 minutes.
• Remove from oven and drop the pan from about 6 inches onto a hard surface. ***
• Cool upside down.

My two failed attempts involved using:

1. a water bath and a loaf pan (with parchment extending the walls) instead of an angel food pan
2. a steaming tray (half sheet pan with water) on the rack below the cake, and a springform pan (again with parchment).

Both of these attempts resulted in cakes that had not cooked all the way through the bottom. and collapsed within seconds of coming out of the oven.

Of the third attempt, I did get a nice, lightly, subtly sweet cake. It's something like the texture of an angel food cake, but with more of a pound cake flavor (from the yolks, I assume). Still, it loses volume, and I can't keep that nice domed top that I've seen in the videos.

Questions

1. Is collapse inevitable? The Angel Food Pan retainted about 2/3 of its height. (But was at least cooked through) How can I keep maximum volume?
2. Is there something wrong with my technique or ingredients? I'll point out: I've replaced 80 mL of milk with 90 mL of half & half; I've added the cream of tartar because that is a standard technique I've learned when whipping egg whites; and I've added the baking soda to offset the acidity of the cream of tartar and to help with lift.
3. Is there a benefit to the steaming or water bath? How should I use it without getting an uncooked center?

_Footnotes

*_{The recipes have called for milk, but I don't keep it on hand.}

**_{I have no idea why some of the recipes I have seen do this. My next attempt will likely avoid heating the oil.}

***_{Supposedly, this helps prevent collapse? I've seen it in the videos, anyway.}