Tails mac spoofing

I noticed that Tails only spoof last 6 (if I’m not wrong) numbers of MAC address.
Is it my computer’s faults, Tails or spoofing limitation (which means it is not possible to change first numbers of MAC?

Thank you in advance!

The first 6 charcters in the MAC specify the hardware manufacturer and, to be convincing, need to match a manufacturer assignment. Indeed, it would be clever if tails selected randomly from manufacturer assigned values for the first 6 digits, then produced random characters for the last 6 digits.