How can I control the duration of a song?

So for boss battles I like to play the Boss Music (example), but the Music only plays for a short while then stops. What's more, the length of time it plays for is inconsistent. I'm not sure if this is just an oversight in the game, or if I'm doing something wrong.

How can I control the duration of a song in Super Mario Maker?

It seems to be controlled by distance from the tile.

However, if you have multiple music tiles, the music will continue playing (without the starting effect) as long as you're within 1/2 to 2/3 of the screen from the last one you touched.

Note: For boss music, you can attach the music to the boss themselves. As long as the enemy is within range and not dead, the music will play.

Since bosses tend to follow you, this works pretty well.

If you attach the mini-boss music to an enemy (say, Boswer Jr. or a Hammer Bro.) it will continue playing until that enemy is dead.

This is the opposite behaviour of the other sound effects that play when the enemy dies.

For the sake of completion: You can also attach music to Mario, and it will play throughout the level.