This is a great news! But still get the same issue:
Wrote 764240 bytes (471705 compressed) at 0x00120000 in 11.0 seconds (effective 555.0 kbit/s)...
it’s a byte smaller, though 
I’ve activated the boot logs and I see the following:
D (259) boot: Trying partition index -1 offs 0x20000 size 0x100000
D (265) esp_image: reading image header @ 0x20000
D (270) bootloader_flash: mmu set block paddr=0x00020000 (was 0xffffffff)
D (277) esp_image: image header: 0xff 0xff 0xff 0x0f ffffffff
E (283) esp_image: image at 0x20000 has invalid magic byte (nothing flashed here?)
E (291) boot: Factory app partition is not bootable
D (297) boot: Trying partition index 0 offs 0x120000 size 0x100000
D (303) esp_image: reading image header @ 0x120000
D (308) bootloader_flash: mmu set block paddr=0x00120000 (was 0x00020000)
D (315) esp_image: image header: 0xe9 0x06 0x02 0x02 40082094
And the app starts correctly… It’s not exactly what I expected, but now I starts, at least.