CST-Electric field above the PEC reflector

Hi , I am trying to capture correct electric field above PEC reflector. Biconical antenna and field probe are placed above the reflector with the separation of 10m. Frequency range is 30MHz to 300MHz. Antenna is placed 2m above from the reflector. the probe is scanned from 1m to 4m with 0.5m step-width. I run the TLM solver, and field is not correct what I received in MATLAB. it's simple two ray theory. the simulation setup is simple. I am curios why I am unable to capture the correct field ? PEC reflector size is large enough (13.6 m x 20.8 x 8 m). Biconical antenna is place on the symmetry axis. CST Studio SuiteElectromagneticsTwo ray theoryradiated emission