Hi Dave,
Greetings from Syncfusion support.
We have analyzed your query to increase the width and we would like to
inform you that on vertical mode both the header and content section are rendered
within the e-gridcontent. So that it is not feasible for us to customize
the header alone in vertical mode. Instead, you can set the width to the Grid
container based on the width the header and content will render.
Please get back to us if you have any further queries.
Regards,
Keerthana.