How to only get shaped strand drops? (Or increase the chance)

I remember reading somewhere that your atlas determines what maps you get, but I don't understand how I'm supposed to control said atlas to get it.

I just shaped my map and I've done every map tier up to 11 except for the following;

Hall of Grandmasters (T9)
Putrid Cloister (T9)
Vinktar Square (T10)
Precinct (T11)
Chateau (T11)
Perandus Manor (T11)


I have not touched T12s or higher.

You have to delete every map tier except the one you want to drop. For deleting a map you need 3 Sextant of the map color you want to delete and an orb of scouring. So if you want shaped strand as only T11 drop you have to seal every other t11 map. As example you play a T10 shaped mesa and you get a t11 map drop, the only available drop now is strand because mesa have no connection to other t11 maps.

So I have to seal every single T11 I've done, and then run nothing but T10 Mesa's?

The Mesa was only an example other Maps which are able to drop t11 are fine, if you have sealed the other t11. Mesa is more likely to drop Strand cause it is a t 10 map with the benefit of no other t11 conected to it.