just focus on the middle x, i've gotten around 30 dragonballs to drop for me there.. if you want to speed up, the dragonball drop rate, after you clear out the field, hop channels, clear out that field, hop back to your old channel. if any dragonball mobs, kill them, then.. rinse and repeat.
I got 4 dragon balls one week. Then 2 weeks of no drops. Finally after 3 days I finally got the last 3. All using these methods described in this guide. I did find a nitch in my hunting strategy which helps the dragonballs to drop more often, which I don't think is described in this video. My next db hunt with my other character I got 4 dbs in one night. Followed by 2 the next night. 2 nights later I get my last 1. After turning all 7 in i went back and got 3 more dbs.
Simply follow this guide and your sure to get dbs. Don't be discouraged if none drop on a db hunt. Keep vigilant even toward the last minute. Surprisingly dbs can drop near the end of a hunt.