Hello Dave ,
I tested your code and I attached a screenshot which shows the result when I run it on my side.
You have not set the RadToolTip's Position property which determines where the RadToolTip has to be shown. Please also note that if there is not enough space to show the tooltip at certain position, it will automatically recalculates its coordinates and reposition itself.
I suggest to examine this online demo
which explains how to configure the RadToolTip.
In case this does not help, please open a new support ticket and provide some screenshots with detailed marks and explanation of the desired position of the tooltip in a particular case.
the Telerik team