I'm using Scintilla in Anjuta and a calltip is used to display function definitions when you write a call. The calltip is displayed just below the function call which is over the arguments you are typing if they span on multiple lines. I suppose this is more common when using GTK as the function names are often quite long.
I write a patch to display calltip above the text as it is done in Gedit or Qt Creator. It looks quite straight forward.
I have seen that this bug has already been reported some years ago with the number 869274. Is there some drawbacks to have the calltip above? We can put it below and move it when the user press enter but it is more work, I don't know if other IDE do it like this. If you prefer I can try to write a patch adding a new message SCI_CALLTIPSETPOSITION (int above) to keep the current behavior by default and allow to set this at runtime.