I'm not sure if that's fixable. Afaik chance to hit is accuracy × target size. If you increase the accuracy, it increases the chances of sniping Infantry as well.
Which if I'm right is only a 0.65% chance to hit at max range. That sounds awfully low for a tank destroyer firing at a large tank...
It's 65%.
0.025 is 2.5% x 26 which is the tiger's unit size = 65% at max range.
Penetration at max range of the SU-85 gun is 180
180/300 x 100 = 60% chance to penetrate at max range.