Conspiring Witnesses – Sabrat HaMaban and the Column

Hello Rabbi,
In your article on the decree of Scripture, you brought up the law of conspiring witnesses and the reason that the early ones gave for the uniqueness of conspiring witnesses based on ordinary denial – in conspiring witnesses, the second sect testifies against the witnesses themselves (the first sect) and therefore they essentially become accused by the second sect (in the words of the Ramban: ). And the reason is because this testimony is against the witnesses themselves, and they are not true to themselves to say, “We did not do this,” since these can say of them that they killed a soul or desecrated the Sabbath.
The question is – what will happen in a situation where the second sect claims that the first sect was really in the same place and at the same time as they claim but – they testify that the first sect could not have seen the murder. For example, they will claim that they (the second sect) (or someone else) hid from the first sect, or that their eyes were covered. According to the explanation here too there is evidence on the bodies of the witnesses and they will supposedly be conspirators but as far as I understand, only by claiming “you were with us” do they become conspirators.