Lazy betta question

I can't decide whether one of my bettas is sick or just lazy. He spends
most of his time either sitting plants near the surface of his tank or
nose-down in the plants at the bottom. He looks fine and eats eagerly.
I've had him since January and his fins have grown nicely and he's not
lost any weight. He eats frozen foods (brine shrimp, mini-mysis,
bloodworms, etc.) or freeze-dried bloodworms once a day.

He got a bit more active after large water changes so I thought maybe
there was a subtle water quality problem - his 2 gal planted tank has a
deep Flourite substrate and I can't gravel-vac because of all the roots.
The water tests fine, but you never know... I moved him into a
different small tank with a bare bottom, and he still shows the same odd
behavior. Now he snoozes on a raft of riccia or rests quietly on the
bottom of the tank.

I tried putting my other betta (the one I just pulled out of the
community tank) next to him and he never even noticed so I don't think
it's loneliness.

Is this laziness normal for some bettas? Is he sick? I've never seen a
betta act like this all the time.

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