Help with flashing Ember 3v2 4.2.2

I would like to flash my Ember 3v2 4.2.2 with klipper. I have built it using KIAUH. But my printer does not eat the firmware. Before getting a different SD-card for flashing, can anybody confirm the following:

1. The firmware hex-file is only 34960 Bytes (which is considerably smaller than the Marlin firmware)
2. The SD card needs to be formatted as FAT32, using no partition works (in linux terms: using /dev/sda for mkfs.vfat is ok)
3. 4.2.2 uses STM32 and an 28kB bootloader
4. An 8GB SD card works

Thanks for feedback on this.