Curtains over return air vents

[TheThirstyStag]

I'm sure this problem is omnipresent in homes with forced air heat and A/C.  My living room has two supply ducts at the top of one wall, and three return air vents on the bottom of each of the other 3 walls.  Two of them are annoyingly below windows that I want to cover with full length curtains that just kiss the floor (or fall 1" above it). 

Does any DIYer here have solid data regarding what covering return vents does to the efficiency of the HVAC system?  Almost everything I read online says that covering them with drapes is a no-no, and to have it drop 4 inches above all vents (this would create an ugly "capri pants" look that my SO would cringe at).   Also, almost all of this advice I read is in regard to supply vents, not return vents. 

I am wondering if it's less important that return vents have an unobstructed path.  If curtains are in front of it, wouldn't it just suck air from the edges and top of the curtains?  Help me understand this, because I'm going crazy hesitating to put up these curtains, and the naked window look just isn't working!

[rulesofacquisition]

It's possible the return side of the system is larger/has more returns than it needs - in which case the curtains won't matter anyway. Probably very difficult to figure out online. If the curtains suck fast to the returns its probably a bad idea, if they don't your probably OK.

[lthenderson]

I've never been in a house with return vents on the floor next to windows. However, I have used the following for exhaust vents on the floor near windows with long curtains to direct the airflow into the room. They work well and have magnets on them to hold them in place. They also make them in a variety of sizes for different sized vent openings.

https://www.amazon.com/Deflecto-50-Premium-Unbreakable-Deflector/dp/B00009W3G7/

[RetiredAt63]

Here as well the supply vents are under windows, to keep the windows warmish in winter.  Return vents are typically located well away from windows, and in a wall at floor height, not in a floor.

[triangle]

Of course it is your call on how to decorate. But I would not consider shorter drapes, ones that covered the full length of the window glass but stopped at the window sill to create a Capri pant look.  Perhaps if the window sill and casement were painted in a complementary color to the walls and drapes (usually white), things would still look good and well put together. This might also necessitate changing the rod above so that the drapes slide over when being opened versus remaining more or less stationary to be gathered back and tied by hand, as the second approach may require longer fabric length to look as good when open.

At a minimum I would install deflectors as mentioned above to minimize the obstruction.

[TheThirstyStag]

Thanks for the thoughtful replies.  I floated the idea about the deflectors to my SO and she's not a fan of the look.  Perhaps I should at least do rulesofacquisition's suggestion of seeing how heavily they suck the curtains in.  IIRC, there's enough suction to hold a light plastic bag, but I don't remember it being aggressive.