Comment 5 for bug 1297695

Thanks for the screen shot. This is actually close to what v1.0+ was meant to look like. Before v1.0, the keyboard used to stretch from side to side even on 21:9 monitors, for an awfully distorted appearance. Now there is an upper limit for the aspect ratio change, i.e. by (Ubuntu) default, for the given height it won't use more width than you see in the image.

Maybe this aspect limit is set too low and we should allow for more distortion, but I think the real problem is that there isn't enough vertical space for the keyboard. The height is controlled by unity-greeter.

What you can do now is to manually change the range of allowed aspect ratios. Create the file
/etc/onboard/onboard-defaults.conf
and add the lines

[main]
xembed-aspect-change-range=[0, 1.6]

If it's still too small for typing then increase the upper limit "1.6" further. Let me know what you settled on.

The Ubuntu default is currently
xembed-aspect-change-range=[0, 1.15]