Hi Tony,
Thanks for using Syncfusion Products.
No, it's not possible to increase the height of the XpTaskBarBox directly. Because XpTaskBarBox height increased depend upon the item added in the it.
If your intension is to increase the height of the XpTaskBarBox mean, please add the panel inside the box and you can increase the height of the panel using PreferredChildPanelHeight property.
Please have a look at the attached sample.
http://websamples.syncfusion.com/samples/Chart.Windows/F62626/main.htmPlease let me know if this helps.
Regards,
Rashidha.