First off, your Goliath has a thermal sensitivity of 110, which means it can detect a 1000 signature at 110M km. those ships have a thermal signature of 960 which means they can be detected at 960/1000 * 110 = 105.6M km.
Second, armor damage for missiles penetrates on square values. in order to go 3 deep a strength 9 warhead is required, the extra damage above four thus bled to the sides rather than penetrating deeper.