I am unsure, but think most of the pioneer "forts" had 2 rows of timbers in the palisades, sometimes 1, but usually 2. The second row timbers placed in in the saddles of the first. Makes the construction much easier in many ways.
If a palisade was part of the blockhouse design, the blockhouse overhangs were extended another foot only on those wall with a palisade, a 3- foot overhang, allowing the blockhouse to view and "protect" the adjacent palisade walls. Two blockhouses in diagonal corners was kinda the "perfect" setup - all 4 walls can be protected. Unsure about when these features became standard, but think I remember reading about this set-up being common in Indiana at least.
If a palisade was part of the blockhouse design, the blockhouse overhangs were extended another foot only on those wall with a palisade, a 3- foot overhang, allowing the blockhouse to view and "protect" the adjacent palisade walls. Two blockhouses in diagonal corners was kinda the "perfect" setup - all 4 walls can be protected. Unsure about when these features became standard, but think I remember reading about this set-up being common in Indiana at least.