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I guess I'm not clear on what the question is asking.
Many TV stations use directional antennas. Even though some people might refer to a transmitter as a "1000 kW" source, it does not mean that it emits 1000 kW of power in all directions. The "1000 kW" is usually in reference to the max emitted power from the antenna in its strongest direction.
The "effective" power being broadcast in your direction depends on your location relative to the azimuthal (compass direction) and vertical location within the antenna's radiation pattern. Most ERP variations are dominated by the azimuthal change in antenna pattern because there is negligible change in the vertical direction when you are miles away from the transmitter (a few 10s of meters change in elevation makes almost no difference when your distance to the transmitter is 10,000 meters or more, which ends up being much less than 1 degree of angular change).
The azimuthal changes in antenna pattern can be far more noticeable. If the broadcaster is using an omni-directional antenna setup, the ERP will be nearly constant everywhere you go. However, if the broadcaster uses a highly directional antenna, the ERP in "off axis" directions can be significantly less than their peak ERP.
The ERP alone does not take into account terrain blockage. The propagation modeling takes the ERP as a starting point, and then factors in terrain effects (blockage, diffraction over ridge tops, Earth curvature, etc.). This is how the tools figure out the available signal strength at your home.
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