I have noticed the same thing I'm 16 weeks and I feel the baby most when I'm sitting or laying down.
The movement from your body soothes them and makes them sleep
Movement def lulls the little one. When im at work and on my feet all day, I dont feel him when I get home and lay down I have an internal drummer boy
Now that I'm 15 weeks I feel a lot of flutters and today I've been up and down all day and I didn't feel my baby till laid in bed