For some reason, the window has a minimum size of 1319x610 on my system.
Same for the volume control preferences, with a minimum size of 1145x232
The reason is the impressive
Capture - Monitor Source of ALSA PCM on hw:0 (STAC92xx Analog)
[alsa_output.pic_8086_27d8_alsa_playback_0.monitor] (PulseAudio Mixer)
in the device combo.
Here is a patch that ellipsizes the device combo in gnome-sound-properties.
Created attachment 151000 [details]
Fixed in 2.18.0-6.fc7