Engines,
I understood the issue with the AV-8B in GW1 was the nozzle locations at the middle of the fuselage. All AV-8Bs hit by manpad were lost, whilst all F-18s which were hit survived.
Aircraft Survivability
........F/A-18 experience in Desert Storm provides valuable information for assessing fighter aircraft vulnerability to MANPADS. Additional information is available from F/A-18 joint live fire (JLF) tests conducted about 1990 at China Lake, California. Combining these data provides insight into the vulnerability of fighter aircraft and helps identify potential vulnerability reduction concepts.
In Desert Storm, four Marine F/A-18s were hit by MANPADs, and all returned to base safely. All impacts were in the engine bay, on or near the “turkey feathers” of the exhaust section. One aircraft with severe damage to both engines’ exhaust sections was able to fly 125 miles to a recovery base. Two of the aircraft lost one engine, demonstrating the survivability of a twin- engine design. By contrast, four single-engine AV-8B aircraft were hit, and all four were lost.............
The vulnerability of the AV-8B was
recognised by the GAO back in the 80s during design:

.......Engine thrust for the AV-8B is provided by a thrust vector- ing nozzle system. The engine has four rotatable nozzles which are mechanically interconnected. The nozzles, which protrude out from the aircraft, emit infrared’signatures which, in some cases, allow the AV-8B to be tracked and fired on from maximum missile ranges. Also, missiles travel faster than the AV-8B, further increasing its susceptibility. According to the Navy, counter-measures are not an adequate solution to this problem.
OPPORTUNITYEXISTS TO ENHANCE SURVIVABILITY
According to the Navy, it is less costly to design survivability into an aircraft than to modify existing aircraft for survivability. Navy officials acknowledged that it is possible to make many of the survivability improvements to the AV-8B before the aircraft goes into full production. They noted, however, that the changes necessary to enhance survivability will increase program costs and will diminish aircraft performance..........