I installed 51.1.A.11.51 and also downloaded the 51.1.A.11.51 twrp files but still can't boot in to the recovery . I get stuck on SONY logo and a blue led then i use they key combo to restart the phone and it boots in to android normaly. I use the "fastboot boot twrp.img" command to get in to the recovery.
EDIT: Never mind i figured it out myself
You have to flash it to the boot partition and then when you power the phone you should hold the volume down and boom you will be in the recovery
WARRNING EDIT2
Do not flash it to the boot partition. You will be able to enter recovery but it will bootloop your phone so I am back to where i was figuring out how to install the recovery
Just follow the bootloader hint on the first page.