It sounds like you are creating the articulations as "character" articulations. For this kind of work I would use "shape" articulations, since you can include both parenthesis characters (left & right parenthesis) in one shape.The following directions are based on
Options menu - Measurement Units - Points:
1. Articulation Designer:
In the pane Positioning:
check "Center Horizontally",
in the pop up menu, choose "On Note Side",
Default Vertical Position: zero
Click the button "Handle Positioning...", and set these values:
5
-3
5
3
In the pane Symbol Options:
When Placed Above a Note, use the Main symbol
When Placed Below a Note, use the Flipped symbol
In the pane Symbol:
Click the radio buttons "Shape" for both Main and Flipped.
Now click the button "Main...".
In the Shape Selection, click "Create...".
You end in the Shape Designer.
2. Shape Designer:
The first problem is to choose parenthesis characters. I use Maestro 24 as my Default Music Font, so my natural choice is the parenthesis characters in Maestro 24. But you can pick any font. If the parenthesis characters in Maestro 24 are "curving" too little for your taste, try EngraverFontSet 24.
Shape Designer menu - Select Font...
(Maestro 24 or whatever)
The next problem is to position the two characters relative to the Origin (0;0).
For Maestro 24 I have found that these positions look right:
Click the Shape Designer's Text Tool.
Click at (-9; -2), and type the ( character.
Click at (5;-2), and type the ) character.
Finally, switch to the Shape Designer's Selection Tool, select all, and group the two elements (i. e.: Shape Designer menu - Group).
When you have finished, click OK, to return to Shape Selection. Remember the number of your new shape, and click Select.
Back in the Articulation Designer, click the button "Flipped...", and select the same shape for the flipped symbol.
That's all.
This articulation works for notes without an accidental. For notes with an accidental in front of it you need to create another articulation where the ( character should be positioned at (-16;-2). You can save some steps by duplicating the existing articulation and editing the duplicate.
Peter