How long have you had Ducky?
If it`s only been a couple of days, from my own experiences so far.....it took my Betta Lamai about 3/4 days before he began to adventure out into the tank. He also stayed pretty much tight to the walls behind the filter or the heater with his fins close to his body....basically looking miserable. I planted the back of the tank with dense plants to encourage him out and it seems to have worked.
However, my other Betta Chimlin was quiet, hiding away and also quite miserable, I made the mistake of thinking he too was just stressed and needed some settling in time.....I was wrong! It turns out that Chimlin has ich/whitespot quite badly. I shouldn`t have dismissed the fact he was quiet and hiding away so easily.
Have you been able to have a good look at Ducky to see if there`s anything that may show he`s poorly or suffering with anything?
It may be that he`s still settling in but I have no doubt others here will be able to give you much better advice from experience than I could.