I wasn't referring to the damage the explosion might have done to the plane, I was thinking about the explosion being more likely to be triggered if the landing gears of taxiing planes pass directly overhead rather than at a certain distance. Then again, since the ground under the taxiway is already compacted, any mechanical effect that reaches a buried bomb is probably vibration rather than direct pressure, and that also has an effect at some distance (but it's probably still stronger directly underneath)