"(▲ means he's higher, ■ means same altitude, ▼ means lower)" isn't particularly useful in actual gameplay, especially on maps like flint county,los santos,bone county, because the ground map itself isn't flat and has multiple raised terrains of various heights well above ground level.
Without proper altitude intel, you won't know whether president is just on a higher ground plane or on a building or heli surfing or wayyyyy up shamal surfing. Each requiring different measure. Since airport distance in particular are far from each spawn, its relatively time wasting to test each measure and waste minutes figuring out the exact method being used.
YoMama's solution is only applicable to flat maps like LV. And if he is shamal surfing you NEED to know an intel altitude or pause and check map constantly to gauge if his speed is too fast while being up. Because intel doesn't mention nearby vehicles or altitude and will say presi is on foot X distance away.