I do a lot of FHG, I only do small wall hanging and nothing larger then a twin sized quilt. I no longer use a long arm as it bothered my bad so bad. I use a Janomi 6500 that has a little larger bed. There's another issue besides tension. You should to use the same weight thread in the bobbin that you use on the top! Weight of the tread can have a lot to do with this too. If you use clear try to use Polyester and not nylon, with that use a needle with a larger eye and in this case you'd loosen the tension top and bottom. Bobbin thread tension should be a real low number. More information then you asked for but if you use metallic threads or the clear use a Schmetz Metallic Needle 90/40.
I'll post one of my table runners in the pictures...
Hope this helps,
Crissie