I agree with you, but I would accept #4. #2 is terribly awkward.
Which are correct:
1-If I knew what he needed, I could help better.
2-If I knew what he needed, I could better help.
3-If I knew what he needed, I could help him better.
4-If I knew what he needed, I could better help him.
Meaning: I don't know what he needs and therefore I can not help him properly. If I knew what he needed then I would be a bigger help to him.
I do not particularly like "2" and "4". The position of "better" in them does not seem natural to me. But maybe putting "better" there changes the meaning of the sentence slightly?
It is good to see you back.