It is not very complicated, to my somewhat limited knowledge. Any vector that comes into contact with the AIM diffusion field that is generated by Accelerator's body is immediately controlled by Accelerator, in any way that he can calculate.

In my opinion, that is very simple.

One application of this power is vector reflection. Which for Accelerator works constantly, and without conscious thought. This is because the necessary calculations are very simple. All that is required is that he add a negative sign in front of the vector. Whether or not that number is 1 or 100×10¹⁷, or anything in between, is irrelevant. The necessary calculation is still as simple as adding a little negative sign at the beginning and bye-bye vector.

Technically, there is a way around this. By altering the path of a vector at the moment it enters into the AIM diffusion field, the reversal will reflect the vector back towards Accelerator. Now I am not that familiar with the source lore, but this weakness always seemed weak to me.

From the official wiki)

Things such as light, sound, and gravity are calibrated to pass through this field for his convenience, though he can undo this if he chooses to.

Which seems to indicate that while his redirection is on by default, it is still subject entirely to his will. Meaning that he could simply decide not to redirect the incoming object at a time. And regardless, to my knowledge, he could simply change the value of a vector from a given number to zero. Whether 1 or 100×10¹⁷, it should not matter. Either are subject to his will.

TL;DR - His powers are not that funky. That are consistent and quite simple.