It improves up to 400px and then the same amount remains chopepd off after that. I tried a few sizes up to 1500px.
This is for 400px and you can now see the bottom arrow but another element below is truncated that was previously not visible at all.
https://www.theonetruevlad.co.uk/wp-content/uploads/2015/05/FB-Widget-400px.png
Currently the option is set to the default that appears when cahnging the tick options, so 432px.
It also looks like changing the tick box settings for showing faces and wall etc makes no difference either. One part is chopped off at the bottom.
Additionally on the Twitter widget the height option has no effect at all when being changed.
I tried with each widget alone as well as the current setup for both with no change to these issues.
I deactivated and activated Jet-pack which looks like it reset to default all the settings. I just connected to Wp.com
This is happening on Firefox, IE and Opera.