In cancelation it said we need to cancel after declare and before movement. But for activation it just said we can prone when use movement. So does it mean that I can move 4 inch then prone when finish move?
No. When a Trooper performs a Skill or ARO with the Movement Label, or when moving as the result of a failed Guts Roll, its player may indicate that it will go Prone. By doing so, any Movement performed will be executed while Prone, with the resulting reduction to the Trooper's MOV and Silhouette values.