Modifying AutoShape adjustments
You want to modify the "yellow diamond" adjustments on an autoshape but it's impossible to do the job precisely because the adjustments don't snap to the grid or to guidelines.
VBA to the rescue.
This macro shows the "adjustments" available for the currently selected shape and the current value of each:
Sub ShowAdjustments() Dim oSh As Shape Dim lCount As Long Set oSh = ActiveWindow.Selection.ShapeRange(1) With oSh For lCount = 1 To .Adjustments.Count MsgBox "Adjustment " & CStr(lCount) _ & vbCrLf & CStr(.Adjustments(lCount)) Next End With End Sub
Then you can use this to modify the adjustments:
Sub SetAdjustments() Dim oSh As Shape Set oSh = ActiveWindow.Selection.ShapeRange(1) With oSh .Adjustments(1) = 0.66 .Adjustments(2) = 0.66 ' And so on for add'l adjustments End With End Sub
See How do I use VBA code in PowerPoint? to learn how to use this example code.