Interesting , brother pops .. different strokes for different folks.
I've been recommended AGAINST a hammer drill, but just get the proper carbide tipped masonry bit and take your time. Use wide masking or painters tape on the tile, mark the spot, tap it with a punch LIGHTLY for a starter to prevent slippage, and drill slowly at first, increase speed and use medium pressure
Also, while drilling between tiles may be easier to get through, it risks chipping or cracking two tiles at once, ... Better to center all the holes on one tile.
Also, ceramic and porcelain generally require different bits because of the differing hardnesses.
If the bar is eighteen inches, it CAN be installedon an angle to be able to center on the sixteen inch stud separation, depending on the need of application. My shower has an eighteen inch bar, but vertically installed at the front outer section for a grip to get in and out, and an angled smaller bar on the inner wall above the soap holder. Pretty handy.
Anyway, God bless you, brother, ... Considering your named 'thebuilder' I'm sure Wilhemina can trust your advice too, and it's a blessing just to be able to share ideas with you here.