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Setting too many constraints can cause problems as the cell size & size smoothing conflicts with the edge sizing. Getting inflation mesh around reflex angles as you near & exceed 270 degrees tends to become difficult. 

You're kind of on the right track with the surface decomposition, but you've focussed on getting a block mesh and not on how to help the inflation mesh whilst also accounting for shocks and separation. I can't tell you how to do this as it's getting into the "engineering knowledge" domain; I can suggest having a look at some of the older methods we used for mesh decomposition (O-grid and butterfly mesh) for some ideas.  The other option is pave and an awful lot of adaption.