Low sales from smaller phones is more likely because the smaller phones aren't just smaller, they have fewer features.
It's not an apples-to-apples comparison. Going from a 6 Pro to a 6 doesn't just mean it's smaller, it means going from a 120 hz screen to 60 hz and losing the telephoto camera, ultrawide front camera, 512 GB storage option, and ultra wideband support.
Going from a Pixel 6 to a 6a gets a lower-quality, 60 hz screen, loses the 256 GB option, and gets only a 12 MP front camera.
Put all the features of the 6 Pro into the 6a form factor, and THEN you can have the apples-to-apples comparison and decide if people actually want large phones.
Your best bet might be Samsung Galaxy S22.