Low?  They are taking it all, if they are scammers! I don't  even trust letterhead to be always legitimate orgn correspondence.   You can print up anything on a computer.  I don't  even contribute to any charity, by mail, esp w a P.O. Box, until I ck address out w Better Business Bureau, or know it's  from one I've  been donating to for yrs!
Sorry, but I don't  trust anyone  solicitating now days, so I ck them out and BBB will tell u the % going to the cause & what they consider acceptable, which like u said is about 65%, which I think is really too low. 45% going into fund raising/overhead is a lot.  In fact when I worked for the BBB doing Public Relations work,  the acceptable was a tad higher!
What u are doing is smart & works!