Priori Incantatem: Why fly?

[frantyck at yahoo.com]

No: HPFGUIDX 30024

When the Priori Incantatem effect kicked in between Voldemort's and 
Harry's wands in GoF 34, why were the two duellists lifted 
involuntarily off the ground to another patch that was "clear and 
free of graves?"

Upon reflection, I find that phrasing highly intriguing.

It's almost as if the two wands were seeking neutral ground. Only 
after Harry and Voldemort landed in the new spot did the golden 
thread connecting the two wands splinter into the web that enclosed 
(and protected?) them.

This limited explanation apart, why fly? Why this particularly 
dramatic and not *evidently* necessary device in a tight and fast-
paced chapter?

(Consider also that it doesn't translate well in visual terms. If 
Rowling sees in her mind's eye what she writes, so do readers. This 
bit, though, I fail to visualise every time -- it comes out a bit 
Disney.)

Help!