Take a look at Wesfarmers for example. They had a entitlement offer @ 13.50 at the time the share was about $16.00. The offer closed on 23 Feb and the share price was just under $17.50. The share is now $18.85 which is a cool 40% return so far.
So no, a share offer does not necessary reduce the share price if the benefits of the raising the capital outweighs the dilution factor.