You can believe what you wnat about the reaper on Rannoch. I will stick with what I believe.
Here's what the Turians did
When Taetrus fell, the turians knew little about the Reapers except that they wanted to enrage the turians. Staying calm, the turians massed in force around Palaven, their homeworld. Fleet Admiral Irix Coronati, in what became known as the "Fifteen-Minute Plan," stationed only two carriers, Undaunted and Resolute, near the system's relay. When the Reaper fleet emerged, the carriers launched swarms of unmanned fighters and spy drones. These were quickly destroyed, but the drones transmitted vital data on the Reapers' effective range, fleet composition, and exact location. The turians' other ships then deployed to defend the system in earnest.
Knowing that the Reapers' weapons had a longer effective range than any of his own, Coronati made a short, daring FTL jump--landing his dreadnoughts in the middle of the Reaper fleet. The dreadnoughts then turned to line up their main guns on the Reapers, which also needed to turn to fire on the turians. This ploy used the Reapers' size against them--because they could turn faster, the turian dreadnoughts locked targets first, and their concentrated firepower downed several Reaper capital ships.
Well, being that what you believe is wrong then ok..whatever floats your boat. Anyways so they made a FTL jump. "Daring" doesn't mean it's always going to work which is probably why you don't see it more often. If they tried that during the trip to Earth, it would've probably been disastourous. However, you did pretty much prove my point. They need the speed and the firepower to do it. Just shooting them in the backside isn't going to automatically kill them because they'd have their kinect barriers up. What happened is exactly what it says in the Codex about the Reapers. Dreadnoughts overloaded their barriers and were able to kill them. Speaking of the codex, I see it now where it mentioned your whole "attack from behind" bit yet I see you didn't notice why it says that isn't a smart thing to do
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Although clearly technologically superior to the Citadel forces, the Reapers have experienced casualties in the battles across the galaxy. This indicates that, theoretically, with the right intelligence, weapons, and strategy, the Reapers could be defeated.
Unlike the mass effect relays that they created, Reapers do not have quantum shields. Locking itself down at a quantum level would leave a Reaper unaware of its surroundings until the shielding deactivated. Instead, Reapers rely on kinetic barriers.
In the case of a Reaper capital ship, these kinetic barriers can hold off the firepower of two dreadnoughts simultaneously, but three clearly causes strain, and four typically results in destruction. Weapons designed to maximize heat damage, such as the Thanix series, show better results against the Reapers than pure kinetic impacts.
The barriers of a Reaper destroyer are less formidable than those of a capital ship. It is possible for a single cruiser or many fighters to disable or demolish a destroyer if they can get within range before they are themselves destroyed.
The Reapers' energy sources are not infinite. For example, to land on a planet, a Reaper must substantially reduce its mass. This transfer of power to its mass effect generators leaves the Reaper's kinetic barriers at only partial strength.
Sovereign was destroyed while assuming direct control over Saren. The feedback from Saren's death seemed to entirely overload Sovereign's shields. Current Reapers do not seem to suffer from this design flaw.
Reaper capital ships can turn faster than Citadel dreadnoughts, but to do so, they must lower their mass to a level unacceptable in combat situations. Consequently, it is possible for a dreadnought to emerge from FTL travel behind a capital ship, then bring its guns to bear faster than the Reaper can return fire. This is a poor tactic, however, against Reapers flying in proper formation."
So yeah, hitting them from the backside isn't a guaranteed strategy whereas they have a better chance of nailing them in the firing chamber