I also have wide windows in 1960s home. If do change windows (single to double) they have to be custom since they so big not regular size. Let me know of a pro answers you. I love ideas. I have blinds in mine but use two so not just one long one. Ours thicker blinds.

I'd be inclined to bring that forward to inside top forward edge of the casing. I see curtain brackets.....?

This is ONE window and where? In what room?

Take some more pictures in daylight of the whole space? Include with shade UP!!

I would have installed them in the same position you show in the photo.

Show a photo when the cellular blinds are open ... they probably "disappear" the most when closest to the window.

Actually at forward? They probably "read" as casing on the window. : )

closer to the window pane.

Hey, thank all of you. @JAN MOYER @chispa see the new photo taken during daylight, the cellular screen is up. It seems we have more space with the current installation?

Pretty window, pretty view. It's probably fine as is.

The only thing I can suggest is do a hold up- just take it out of the brackets, keep it all tight and up position , have a "holder" and look at it straight on view at forward position flush .

"More space" for what? It's the same size no matter the mount: ) ?

Thank @JAN MOYER! What do you mean "keep it all tight and up position...? ", I think will keep the screen the way it is then. (more space, means during night when screen is down, we still have some space of the sill, i.e. not blocked by a covered screen)