Another thing you could try, just to see the result, is to toggle the arrows out and see if the "tail" shrinks. I think there must be something wrong with how Alibre "reads" the dimension text size and how it fits between the extension lines. I've always had the problem with the "smart" dimensions not flipping the arrows when the text gets close to them. It seems the arrow leader is not calculated for when to "flip" the arrows out.