Actually I have to set labelWidth = false for labelStyle to work:
For my purpose, where I just want fields to be laid horizontally next to each other, I think the solution's fine:
labelStyle: 'width: auto'
Specifying the width for the field just affects the field, not its label width. I suppose it's not the cleanest solution since the label doesn't actually explain what the field is, but it makes the code simpler.