When all else fails, you could try this:
On a river, have a dropper about 12" from the dry, with a small, easy sink pattern on it. A Tiny Miracle, P.T nymph, sparse spider or thread buzzer size 20-16 depending on size of dry and current speed. The short distance to the dropper is to help ALL the tippet to sink before the dry reaches the expected taking zone. This method helps to eliminate surface micro drag on the dry too! Excellent when fish are feeding on smuts in smooth glides; a size 18-20 Griffiths Gnat with a size 22-20 varnished buzzer on the dropper.
On still water the distance between dry and dropper can be extended to 18" - 24" as the dry is not subject to a short drift to the taking zone.
Then there is:
The duo method, when the 'dry', O.K. its actually an emerger, is on a dropper, with a weighted nymph on the point, is another way round the problem. The weighted nymph drags the dropper and some of the leader/tippet under.
That's on the river. For still water substitute weighted nymph for varnished buzzer etc.
Then again:
The Roy Christie reverse parachute. The design is intended to sink the tippet by the abdomen being submerged.
All this comes from one who is obsessive about visible floating line, and how accepted 'sinkants' rarely do their job!