"Range" is not an exact science. Everything depends on line of sight. Theoretically, if you put the two side by side with identical power and identical antennas, on water or flat land, they would have the same range. That's the 8 mile potential the walkies have. The 4 miles he told you for the CB is more real life environment, with hills, buildings and the ever present atmospheric conditions.
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It's not that life is so short, it's that you're dead for so long.