Nope, it is not linear.
If according to your calculation with 65 points of score for 0.1283% difference in hp to max hp ratio the score would be linear then you would receive a score of around 0 points while finishing the raid with less then 85%.
85% remaining hp = 15% damage
15% / 0.1283% = 116.9
So reduction with linear decrease as you claim it with 65 points of score for 0.1283% would be:
116.9 * -65 = -7598.5
So the score would result in 0 or at least close to it with only 85% remaining HP.
And that is not the case, is it?
At latest for anyone finishing with “only” 80% of max HP the score would then be 0.
And that is definitely not the case.