The Sweden international is hoping to celebrate his 30th birthday yesterday by playing some part in Albion's clash with Villa on Sunday.
And the summer signing believes his first 90 minutes in Baggies colours in Wednesday's 2-1 loss to Liverpool in the Capital One Cup will help him find top gear.
He said: "I feel better and better all the time but you can still see that the final pass is not there.
"There were too many times on Wednesday when I lost the ball but it's getting better and. I think in the second-half, I came into it better.
"I started well in the first 15 minutes, then I came into the middle and the whole team lost their game, including me. Then in the second half it was more 50-50.
"It's getting better and I found space really well in the second half between the midfield and defence.
"It was just the last pass that was missing."
Rosenberg started the game out wide before moving to a central role in the second half behind main striker Romelu Lukaku.