While it is uncommon, it’s not wrong to see a tweeter below the mid/woofer too, with the mid-woofer at ear level.
As a speaker designer and sometimes maker, yeah, the optimum twetter location can vary quite a bit, based on it’s off-axis frequency response. For instance, a tweeter may rise or ring at the top octaves, while off-axis becomes perfectly flat. Putting the tweeter off axis essentially equalizes it, without actually using more parts, and maintains good off-axis response as well. All in all a win-win.
A speaker designer who takes this approach demonstrates good balance of techniques and better than average contemplation of the drivers being considered. This is a variation on tilted baffles, and speakers designed to be toed in less than average, or not at all.
The speaker designer must take into account while making the crossover and cabinet, but it’s a perfectly good design choice, and in some cases better than the traditional.
Depends. :)
Best,
Erik