[RightDeve]

Imagine a situation this way: you're in a PBeM battle against someone and the rule said "e-mail diplomacy will either mean decisive victory or decisive defeat". That is, if you think you can no longer put up a fight, you have two choices: 1)Make e-mail diplomacy (surrendering, hence decisive defeat), or 2)Retreat to the gray hexes and avoid more losses (so at least you can achieve a minor defeat or even a draw).
Viewed from opponent's point of view, he will either surround your forces to achieve complete isolation and squeeze what last points he can get out of your forces, or, he will continually send you surrender e-mail. (if we assume that winning streak is so important for both sides).

What you said is not generally an encirclement, Marcello. It can be achieved either by flanking, or infiltration. So maybe I can say that FULL encirclement in SP doesnt have any significant effect (unless you're under the situation I stated above) ?