Current
How fast is the current on the day? Start with a lighter sinker and time the descent, if it's taking forever to reach the zone and the drift is over before you get there, then try dropping earlier or increase the weight.
Wind
Is the wind impacting your descent time? Again, with experience you'll get a feel over time for how fast you're drifting, how long it takes to get the bait down and try adjusting your weight till you get an efficient drop coupled with lots of bites.