How many beans did you use? Most recipes i seen call for two for a 5 gal batch.
I would say to get more vanilla flavor, you would have to leave it in the secondary longer. The recipe I looked at said to leave it in secondary for 3 weeks.
I wouldn't think the vanilla will come out more the longer you let it sit in the bottles, but i could be wrong.
The other thing i seen is people will cut the beans lengthwise, scrape out the inside and let it soak in just enough vodka to cover the beans and let them sit for a day.
Let your bottles condition for at least 4 weeks(if you can stand it
). If it still seems flat after that try moving them to a warmer area. I let my bottles carb at 75f for 2 weeks. Then I take a bottle put it in the fridge, wait a day then taste it. If its carbed I move them down stairs to store.(68f-70f). The longer you let it sit the better. Ive seen noticeable improvement after 6 months.