Steam allows you to install in other locations:

I have steam installed on my E: drive - E:\Steam - so if FSX had been installed there, it would be installed in E:\Steam\steamapps\common\FSX

I also have other steam libraries:

G:\SteamLibrary
I:\SteamLibrary
M:\SteamLibrary

So FSX-SE could have been installed in G:\SteamLibrary\steamapps\common\FSX, I:\SteamLibrary\steamapps\common\FSX, or M:\SteamLibrary\steamapps\common\FSX. I chose to install FSX-SE on the M: drive because it's a small SSD (I consider it too small to install the OS on).

As you can see, my Steam games are installed across four drives/partitions.