I have a different idea:

We still calculate the victory point reward the same way, and we use this number to calculate the defensive point loss based on a rank-related ratio.

I try to explain better:

The worst case scenario is that you're rank 1 (or top 5, or 10), in this case your conversion ratio is 1:1, so if you gain 12 points for beating a rank 50 you'll also lose 12*1=12 points for losing with the same guy.

On the other side, because the victory reward remains the same, the rank 70 still gains his 20 points for winning in both offensive or defensive way against someone that is far more high rank.

Doing so, top tier guys will not feel that "1 step forward 3 steps back" sensation so strong, and remaining top tier will still be difficult like it has to be.

The best case scenario can be, a rank 1500 that challenges our top tier rank 1 mr. 10k man. In this case rank 1500=1:0,5 ratio (random number, just an example), so if he loses in any offensive or defensive way, versus a rank 1 he'll lose 20(actual win reward)*0.5(ratio)=10 points loss. And so on.

I don't know if running the numbers that can work, but on a quick thought seems respecting what Sparton wants to achieve for keeping the game away from players frustration and pay-to-win dynamics, it also needs real skill to remain in top tier position because of the 1:1 ratio.

Let me know your thougts.

Cheers