Take into account, the area in which the whistle is blown. A whistle outside will be carried in the air without interference. A whistle in a cave will bounce off the walls, causing echoes, if the wall are hard, such as rock. But, a wall of soft dirt will absorb the sound, restricting the range, especially if the cave path is not straight.
If you have a chance to explore a cave, you can test this out. In the USA, there are guided tours of caves within a day's drive from just about anywhere.
Another concern for the player is misdirection. If the hearer responds and comes running, but comes to a fork in the path, which way would they choose? When I DM, If the signaler sends another blaster when they responder is at a fork, it will be more obvious which way the sound came from.
Of course, chances are, someone or something that the signaler might not want to hear the signal, has heard the signal as well.
Another thing to consider, low tones, such as a horn blow, travel farther than high tones, such as a whistle. This link Low ton vs high tone explains this. This is why fog horns are super low.
Another thing to consider, high tones are used often because the din of constant noise, such as machinery, or groups yelling or talking, mute out low tones. This is why factories use higher pitched whistles for lunch break and end of the shift calls.