Yes whatfly, I recall the same rule of thumb

Quote Originally Posted by whatfly View Post
Cannot remember where I read or heard it, but an old rule I remember is to make the dropper 1.5 times the expected length of the largest fish you were likely to cast. Idea was to minimize likelihood of tangling up the fish when landing, but nothing is going to absolutely prevent that, anymore than tangles can be completely eliminated. As the previous posters said, 18-24" is a reasonable guide for most situations. Keep in mind what you are really trying to do is cover a wider range of depths, so the distance is a function of what you are trying to achieve, not a hard and fast rule. Remember to slow your cast and open your loops, and that should minimize the tangles.