For anyone wondering, the real capture range is 5 + captor's largest footprint size + target's largest footprint size. It is 10 + ... for interrupt pathfinding/stationary units because once the move task is finished, the engine gives 5 more range to be able to capture units that are trying to run away. Footprint sizes are 1x1 for non-experimental land units so that's why the most common range is 7/12.