Fig Tree Planting Depth/Height
In heavy soils and wet climates I would strongly consider planting fig trees higher above grade. However.. you increase your chances of getting hit with a late frost.
This study recommends planting in berms. I think there's a lot of value in it and I've tested similar planting heights in my climate: https://patents.google.com/patent/US7818915B1/en
"It has been found that besides higher density of planting, superior results can be achieved using “berm planting.” Berm planting means mechanically building a sort of a ridge by accumulating the top soil from the space between the rows of the trees into a “ridge” on top of which the trees will be planted. The height of the ridge is normally between about one and two feet depending on the heaviness of the soil with heavier soil requiring a higher ridge. The width of the top of the ridge is about 15 to 25 inches so that a truncated pyramidal ridge is formed. Alternatively the ridge can have a curved (convex) top with a top width of about 15 inches or more. Depending on the top width the bottom width of the ridge is normally between about two and three feet.
The top soil layer is considered to be the most fertile, so that by this practice we concentrate it in the root region. In addition we provide local drainage to the trees, so that the roots and the tree crown are elevated above any standing water from excessive rain or irrigation. The berms also provide earlier warming of the soil/roots in the spring and improved frost protection due to the higher relative elevation as cold air is more likely to flow down and off the elevated fig trees. When fig trees are grown on berms of the type just described, the trees produce superior brebas as well as “regular” new growth figs. Furthermore, because figs grow readily from cuttings, it is possible to build the berms in existing orchards by covering the crowns and the lower part of the trunks of existing trees. These will later initiate roots which grow into the berm."
In my Z7A, 2F low this past winter (2018-2019) two of my trees survived planted well above grade. One is a White Marseilles that had 8 inches of its root ball above grade that was planted in a 1 foot high raised bed in the fall of 2018. Very similar dimensions to the berm mentioned in that study. Another was Teramo Unk which was planted 100% above grade in a similarly sized raised bed in the spring of 2018. Both have wooden sides.
In sandier more well draining soils, I would recommend planting deeper. MP grows his trees to a 5 ft tall single stem whip. Plants the majority of the trunk below grade and the result is a very strong root system in short time.