To avoid 20% ball possession you must have at least 3 players at the back line, at least 1 striker, at least one player on each side (DR/L, DMR/L, MR/L or AMR/L) and never 3 players on one side, at least 3 players in midfield (no 5-2-3 formation)... also you must have at least 4 players at opposition half (ML, MC and MR count)...