BoxHeightOffset: Double;
The BoxHeightOffset property determines callout height.

Executing the example requires that the repository contains workspace with the WSP identifier containing arrow callout.
Add links to the Andy, Drawing, Metabase system assemblies.
Sub UserProc;
Var
mb: IMetabase;
ws: IWxWorkspace;
BArrow: IWxBoxArrow;
Shapes: IWxShapes;
Begin
// Get workspace for editing
mb := MetabaseClass.Active;
ws := mb.ItemById("WSP").Edit As IWxWorkspace;
Shapes := ws.Shapes;
BArrow := ws.Shapes.Item(0) As IWxBoxArrow;
BArrow.BoxHeightOffset := 5;
BArrow.BoxWidthOffset := 10;
(ws As IMetabaseObject).Save;
End Sub UserProc;
After executing the example the callout is resized.
See also: