I think it's a balance issue.
The Fanatic Falcon 159 light wind probably has the finbox way back there compared to modern purpose-built foilboards. Just look at it. If the finbox screws are BEHIND the aft end of the footstrap screws, this will be the case. Modern foilboards have the front fin screw at about the mid point of the back foostraps.
Those big Slingshot snow shovel wings have a very broad center of lift, and so they work just fine with a far aft finbox. I have a i76 in the B position that works just fine with a far aft finbox.
With your AFS the wing is too far aft for balance between your feet. My first foil was an AFS-2 F700 that I mounted on a formula board with a too-far-aft finbox. I could not get it to lift unless I practically stepped off the back of the board. Moving the finbox 3 inches forward solved that problem.
Measure your wing position relative to your footstraps. The wing should be somewhere at or near the midpoint.