The Acacia flat top style/form is typical in the African landscape. Charles Ceronio described the style/form and variations in his book, Bonsai Styles of the World. For those who don't have his book yet - you are missing out!
Here s a sketch from his book of the typical form:
Here is an nice example of a tree in nature:
And flat top can be big trees:
A damaged tree:
Most people are confusing the Pierneef and Flot top style/from. Here is a comparison:
The biggest difference is that the Pierneef splits normally into two trunks. The flat top splits into more than two:
Where the tree splits the branches are relatively straight ending in the canopy:
Here are some generalized proportions as from this picture:
Have fun designing your own African Flat Top Acacia Style/Form bonsai!
(Any observations will be welcomed.)