At Higher Tiers, I found it slim pickings to find Chinese or German tanks. At Tiers 4 and 5 I usually found 4-7 enemy tanks suitable for the mission per battle. To get the Section Rewards you have to switch to a Tier 6-10 tank for the required extra battle. After struggling to find the right tanks to kill for the first 5 kills, after the switch I finished the next 15 in one evening. Tomorrow I will see if this holds true for the Creighton Abrams missions and Tier 5 tanks facing Tiers 3-7.
I think the lower Tiers are filled with a lot of players running mainly German tanks (not seeing many Chinese tanks at any Tier) because they don't recognize the bullseye on them, whereas the upper Tier players do and avoid running the German tanks as often until the mission is over. Just my observation..
Oh, a quick word of caution, pay attention to ally American tanks sitting over your shoulder, Many are not shooting, but waiting for the kill shot. Happens all the time with this kind of mission.