Question on return air grille in basement

I have been living a year and a half in a 4 level split with a hot air
furnace with the addition of A/C. There are return ducts on each floor
including one in the basement at the floor near the furnace. This is
the only return grille that can be open or closed. The rest are fixed
open.
Someone had marked the grille "open for cooling, closed for heating" .
But I think this is wrong. I believe if you open the grille for
heating, it will pull down the warm air to floor level in the basement
making it more comfortable. My supplys in the basement are at ceiling
level, and since I opened the return grille a few days ago it seems
that it does get a bit warmer down in the basement.
The same might be true for summer. My supplys in the house are at floor
level, so the A/C might not cool as well as if the supplys were in the
ceiling. But if I close the return grille in the basement rather than
keep it open, I think that would help the return grille on the top
floor draw more cool air upward, rather than get sucked down into the
basement.
I was just wondering what everyone else did if you had a similiar HVAC
system.

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