One actually can go behind a larger fleet. Its not a theory, its a fact. You can run the game and check it for yourself.
Geometry has nothing to do with that. Problem of the larger fleet is called inertia. Coupled with lack of power it creates a situation when fleet is unable to turn at a rate required to cope with the smaller fleet maneuver while keeping itself as a single formation. It creates an opportunity for the smaller fleet to pick any place and vector for the attack.
While on travel drives the whole combat map is not enough to notice the change of course for any degree. For such a small scale ship is treated as incapable to maneuver. This is why they have to turn the travel drive off to enter combat.
Early warning is not even a factor here. Detected fleet can choose to change its course at any time. Specifically at the closest range when large fleet is fully commited to whatever defensive maneuver it chose previuosly. This is why, any attempt of the larger fleet to rotate in any direction will make things even worse since it will have to fight its own inertia to rotate in the opposite direction. By turning it just presents a better opportunity for the attacker. The larger the difference in sizes the worse things are for the larger fleet. There is no solution here apart from the defensive sphere formation.
Going behind a fleet is NOT the same as hitting the logistics ships. There is nothing stopping a fleet from putting ships behind the logistics vessels.
I spent most of that essay explaining exactly why going to the back of a fleet is not the same as ambushing them.
You don't seem to have an understanding of orbital mechanics. Newton's laws dictate that if a fleet of frigates decides to go speeding in, every second spent accelerating in the direction of the target means another second the attacker has to burn to change direction.
The defending fleet's velocity is relative to the attackers, There is no momentum change to face a new attack direction, simply have the vessels you want in the back accelerate (or stop accelerating) in the direction they want to go. Suddenly, they're in the back. I could make a video to show you exactly how that works.
Compare the speed of a frigate to the speed of a destroyer. In sustained burn, exactly the same. That already negates your little dodge idea, not that it would work.
There is no "sidestep" in space. Once the frigates have chosen a course and set themselves to it, they cannot just zip around an intercepting force. They must commit or build so much sideways velocity dodging around that they will have to set up another attack run. Even if they have the acceleration to do so, the intercepting fleet will be able to see the maneuver as it occurs, and dodge backwards, closer to the fleet and thus saving time as they don't need to go as far to resume the block. In this case, your vaunted inertia works against your frigates.
Now, why would a huge battlefleet even intercept? They have the ships to just keep going where their going and take the "ambushers" on the rearguard. Those exist. They put ships behind the aircraft carriers as well. Since that rearguard is most likely that captial ship's cruiser and destroyer escort, the ambushers would get smashed, because they have to engage in a stern chase, slowly closing ground, while the rearguard could just stop accelerating and metaphorically "hit the brakes" to end up in range. Flanking vessels could slow their acceleration a bit and fall into formation to spread out the guard and resume covering the rear.
Besides which, there is nothing stopping the defenders from making a wall in space. The frigates would have to overshoot or dodge around, then spend a ridiculous amount of time building up velocity to return to turn around and come to attack speed.
Newton is mean. He doesn't let your movie tactics work.