What constitutes anal intercourse? Even though it is a sin to have sex from the back passage in Islam whether it is male or female but how much of the penis should penetrate for the hadd to be applicable. I have read Fatwas on this site as well as many known Islamic sites that at least the glans of the penis must disappear fully. If partly or hardly the tip or urethra is touching it doesn't constitute. Again it is a sin but the hadd is not applied in such a case?
"It is not a condition of repentance that the hadd punishment be carried out on the repentant person. He should conceal himself with the concealment of Allaah, Achieving sincere repentance is better than confessing so that the hadd punishment may be carried out."
Copied from islamqa
"This person has repented well and has given back to people what is rightfully theirs, so he should not let the Shaytaan come and spoil his repentance.In the case of zina, the hadd punishment is conditional upon penetration, which means that the head of the penis disappears into the vagina. If it does not penetrate it or only part of it penetrates it, then he is not subject to the hadd punishment.
It says in al-Mawsoo’ah al-Fiqhiyyah (24/23),."
Copy pasted from islamqa
Using same analogy i think hadd punsihment is only applicable if the head of the penis disappears in anus not giving a fatwa though.