What you are referring to is called the " installation delay". Basically radalt is a timing signal from transmit to receive. Knowing the delay time due to antenna position and transmission cable type, a particular radalt transceiver is adjusted for the signal delay dependent on the aircraft it is fitted to. It is designed to give zero feet at touchdown with the aircraft in standard touchdown AOA. A330 has transceiver at rear of aircraft with the antenna aft of main gear. Boeing have the radalts and antenna fwd of main gear.