why won't Obama debate one on one

There has been a lot of speculation about why Hilary is asking for more debates but Obama is refusing.  I guess the main claim is that he wants to let the voters get to know him, but this makes little sense to me, since debates are televised and he's likely to get mainly supporters at his rallies.  I think he should want to debate one on one, the differences are clearer when both have to answer the same questions and respond to each other. Some say he thinks he'll lose votes with more debates, which seems unlikely to me. Others say he wants to give the perception that he's actually ahead in votes, and that her call for more debates is desparation and not respect for the voters right to get to know candidates better before voting, and that he's more interested in perception than in reality, but this also seems far fetched. So, why won't he?  

There are some possibilities. One is that he has to be nice to her on TV, and his 'base' likes it best when he beats up on her.  One is that he's adopted some of her policies and he doesn't want voters to know he's 'copying' her homework.  One is that he looks worse in debates than when he's reading speeches and he wants to look his best for voters.  Shall we poll?  And, if there are other possible explanations, put them into comments.  I admit Hillary is my first choice and I want to see more debates. I also acknowledge that she's a great debater and the the more people see Hillary, the more they realize that she's more than likable enough, she's a great candidate who is prepared to take over the presidency and lead the nation.