The midrange driver is placed very close to the tweeter to prevent uneven frequency response with peaks and dips due to phase problems close the crossover frequency, where the frequencies reproduced by the drivers have some overlap.
Tweeter at ear height, mid right next to it. If the crossover frequency is low enough, then the bass driver can be placed farther away, such as on 3-way systems with the woofer on the side, back, or on the bottom.