Fishing a dry-fly and using a low-diameter fluorcarbon tippet (0.185mm 8.2lb), the problem has been that although heavier than water, the tippet is too light to break the surface tension.
OK, sinkant helps, but not that much, and requires frequent application. A bit of a nuisance especially when a trout is whelming within casting range.
In a similar situation, trotting the far bank with a float, I'd reach for a small shot to sink the line behind the float.
Hmmm! a small buzzer might do the same job, thinks I.
And so a short-dropper is tied to the tippet with a small buzzer on the end.
One slight modification needed (the buzzer not quite heavy enough, larger buzzer attached).
And another (the buzzer needs to be nearer the dry.
Note to self, experiment with a sliding knot in future).
And it works a treat, the buzzer pulling the tippet down, and a good size rainbow tops and tails the dry as I set the hook

(I love it when a plan comes together!)
The main problem is matching the weight of the buzzer to the buoyancy of the dry, particularly as the buoyancy decreases when the dry has been slimed!