I answered to the same question in your other forum thread, however I am pasting my reply here too:
I am afraid what you would like to achieve is not supported. Actually increasing tooltip's z-index does not help because of the tooltips are in different stacking context. The only possible workaround I can suggest you is hiding the default tooltip and in the show it in the seriesHover event with a custom position (for sample code check this forum thread).
On a side note, I kindly ask you to refrain from posting duplicate questions as we monitor all threads - posting same question more than once produces unnecessary overload and does not direct a faster response. Thank you in advance for your understanding.
Join us on our journey to create the world's most complete HTML 5 UI Framework - download Kendo UI