Airfoilmod
I was allways under the impression that having the HP fuel downstream of the FOHE was a failsafe design. The theory being that if a pipe within the exchanger ruptures the oil is at a higher pressure than the fuel. This leads to the oil contaminating the fuel system but the engine can combust this. Conversely If the fuel were to contaminate the oil system the lubricating properties of the oil would quickly be lost causing damage to the engine.
I Can't remeber the architecture of the GE system so I don't know how they get round this ?