arranging horns

Hey everybody, I'm scoring some trumpet parts and had a question if any of you gurus out there wanted to tackle it. Feasibly speaking, how far apart would the trumpets need to be in order to get a a full sound of harmony. I hesitate giving them all of the harmonies because they're tight. So I thought it would be logical to give them the main line played in octaves and let the harmonies roll with saxes and trombones. Rhythmically they're the same, I just wanted to thicken it up a bit. I appreciate the feed back, please feel free to email me personally so we don't take up zorn-list space. Kasra George Ahmadi