Why Are My Pygmy Corydoras Staying At The Back Of The Tank?

I have 15 Pygmy Corydoras. I moved them to my 20 gal. about a week or so ago. In my 29 gal they used to be front and center and swimming all over the tank.
Now they only stay in the back and swim around the back glass.

I have no idea what caused this change other than the change of the tanks, but the 20 is planted and has cover, just like the 29.

What could be causing this behavior?

Tank Stats.
20 gal.
15 Pygmy Corydoras
9 Purple Harlequin Rasboras
3 Sparkling Gourami's
Amano Shrimp, Mystery Snails and 4 tiny Horned Nerite Snails.
Anacharis. Java Ferns, Anubias, Bleheri, Micro Sword and lots of Marimo Moss Balls.

0 ammonia, 0 nitrite and 5-10 nitrate. Ph 7.2, Gh, 10 Kh, 7.

This is a pic of the tank.

 

New house. They're not comfortable in it yet. Give them time and they should come around.

Also, smaller house. They may be establishing territory away from the other fish.

 

Both good points, however when I added them to the 29 they were all over the tank after 1 day same as with the 5 gal quarantine when I only had 3. They actually taught my SterbaI to come out and play.

I moved some stuff around a bit to add more "cover" to the middle and towards the front. Maybe that'll help?

Don't mind the Betta, he's waiting to be transferred to another tank.

 

Maybe. Fish psychology is complex. I have some pygmies in a 40 gallon that have been there for a year. Just this week they decided to hang out front and center. The tank is heavily planted and scaped, they just prefered lurking in the background.

 

Yes, yes it is. I guess I'll just give them some time to see if they decide it's not so scary to swim around like they used to.