You should be doing this with styles. Set the property of the List Bullet style so that its bullets are the size you want. While you are at it, make the styles font 18pt and Times New Roman.

When you then expand the aRng to the story, what is the style of the other bulleted paragraphs (the ones that weren't in the original selection)? If they should also have List Bullet applied then do that. If they are some other style, change the style definition on them to match the attributes you want to see.

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Andrew Lockton
Chrysalis Design, Melbourne Australia