With certain units having rear support from being deployed in depth (pike, warband) or support from light troops, but DBA neglects to examine a fairly common renaissance heavy infantry combination: pike and blade.
Mercenary companies of Swiss (pike and halberd) and landsknecht (pike and zweidhander) were intermixed units of pike and blade.
One or the other unit type took the forefront depending on the type of enemy they were facing. Pikes handled knights and blade handled other heavy foot.
So I would suggest a deep formation 4pk/4bd.
When facing knights, this formation fights as a unit of deep pike with the same bonus. When facing other foot it fights as a unit of blade with the same depth reinforcement given to warbands.
The combat rules should allow for the mutual slaughter that resulted when two units of these mixed pike/blade formation went at each other - what the Italians called "Bad War".
A pike/blade unit destroyed by a pike/blade should be able to do the same to its enemy one more time before it is removed from the board - mutual slaughter.
P.S. And this unit can also form a square facing outward in all directions when attacked on flank or rear by mounted units (another neglected tactic in DBA).