Team Daiwa Pro Series Bass Trigger Rods

For dry fly fishing, fishing down and across gives you quite an advantage since the fish sees your fly before anything else (tippet, leader, flyline) so they are more likely to take the fly in that scenario. You can also let the fly land above the fish without much disturbance which is another advantage. When you cast a dry fly from below the fish you are much more likely to have the fly, tippet or leader land on or near the fish spooking it. Of course you can definitely still catch them this way, it is just that you have more of an advantage fishing down and across. Getting a good drift from upstream requires better line control because you need to feed line out as the fly floats downstream and if you don’t, it will easily drag. As Marcel said you can also spook them easier from this position so you have to keep a low profile.