Comment 9 for bug 1817097

/etc/mke2fs.conf:
[defaults]
 blocksize = 4096
[fs_types]
 small = {
  blocksize = 1024
  inode_size = 128
  inode_ratio = 4096
 }

We default to 4k, unless one is formatting small filesystems which from manpage:
If the filesystem size is greater than or equal to 3 but less than 512 megabytes, mke2fs(8) will use the filesystem type small.

And in your tests you do appear to use 500MiB big images.

I wonder if we should bump even small ext4 filesystems to use 4k sector sizes.