Why does Ubuntu installer add 33MB of free space at beginning of disk and why is EFI partition 469MB in size vs 512MB?

Question

Installing Ubuntu for desktops 22.04.1 LTS on an external 16GB SSD and trying to make sense of following inconsistencies?

1. create new partition table

   

2. create 512MB EFI partition

   

3. create 15511MB ext4 partition

   

4. check if everything is OK before installing

   

Why does Ubuntu installer add 33MB at beginning of disk? Why is EFI partition 469MB vs 512MB?