Embarrassing hack. The knob looks up three levels for a width.
<div class="col-sm-3" ng-init='volume={"item":"your_control","type":"knob","floor":0,"ceil":100,"step":1 }'>
<div style="width:100px">
<div>
<div><widget-knob ng-model="volume" /></div>
</div>
</div>
</div>