If your intent is to practice using your Jian, as a weapon, which according to Chen Weiming, is to use it for striking and stabbing, then your assessment would appear to be correct. That the extension of the forefinger is to give the practitioner performance for a presentation, as compared to the intent of using it as a weapon.
In This Podcast:
Using a Long Staff as a Tool : Video With Ando Mierzwa
1928 TaiJi Sword Manual : Brennan Translation