The casting technic down and across stream is effective enough. Especially this type is popular among the European fishers. After a cast these anglers not made any manipulations with a line . The current straightens a line, then an leader and a tippet. The fly drifting downstream is developed on the straightened tippet and follows downstream a line on a diagonal traectory . It is possible to define approximately speed of movement of aflyat such technics. Sometimes on a rapid current the fly passes on a diagonal behind a cord about 25 metres of all for 5-7 seconds. 5 meters\5 second!!! At the bad casting technics , the fly operating time is reduced about insignificant 2-3 seconds for one cycle.
One of signs of an existing problem is that fact that the overwhelming majority of attacks occurs in the end of this movement, since the moment when the fly stops on the line that is completely straightened downstream. There are many explanations to it, but the most real consists in that, that only during this moment the fly starts to work and involve a salmon. That is, the fly should be stopped. Proceeding from my practice, the fishers using one-hand fishing-rods, are more inclined to change of the habitual technics and is more often apply mending what to stop or brake fly movement downwards. Owners of two-handed anglers are less inclined to change technics of presentation of a fly. Though technically it is not difficult.
Upstream mending considerably reduces speed of drift , much more increases time of effective work of a fly in water. Hence, the quantity of attacks of a salmon which ignored earlier quickly moving flies considerably increases. Especially the mending technics upstream is necessary for presentation of fly of the small sizes, in the conditions of low water and at catching on a current among stones when we are compelled to investigate everyone separate flow.