Nowhere in the Sunnah does it say to only raise your finger at that point. If you go and read the Hadiths for yourself, you will find this out:
Moving the Finger in Tashahhud
"He (sallallaahu 'alaihi wa sallam) would spread his left palm on his left knee, clench all the fingers of his right hand, point with the finger adjacent to the thumb towards the qiblah, and fix his sight on it (i.e. the finger)."185
Also, "when he pointed with his finger, he would put his thumb on his middle finger"186, and sometimes "he would make a circle with these two."187
"When he raised his finger, he would move it, supplicating with it"188, and he used to say, "It is surely more powerful against the devil than iron, meaning the forefinger."189
Also, "the Companions of the Prophet (sallallaahu 'alaihi wa sallam) used to remind each other, that is, about pointing with the finger when supplicating."190
Once, "he saw a man supplicating with two fingers, so he said, "Make it one, [make it one,]" and indicated with his forefinger."191
"He (sallallaahu 'alaihi wa sallam) would do this in both tashahhuds."192
So you see, the time for pointing the finger starts when you sit in Sujood. If Imam Abu Hanifa has another authentic hadith that supports your position, I would like to read it.