Despite our best efforts, even with a weighted fly, and weight on the
leader, the fly may not get deep enough, or may not drift in a realistic
manner. So, we have to combine some presentation techniques and perhaps add
more weight to the leader. Let's discuss presentation first. One way is to
cast straight upstream, so that your fly and weight and indicator are all
in the same current lane. But, that's a lot of work, you have to gather
line quickly and you risk putting your fly line right on top of the fish.
It's best for short casts. When fishing across the current you can also
mend line, sometimes frequently throughout a drift. But, mending often
moves the fly too much, and it's better to get that upstream loop of line
before the fly hits the water with a reach cast. Keep trying different
approaches until you find something that works.