Jammedstab,
Your statement about asymmetry is incorrect.
If you have a Slat Primary Fail, only the Slats have reverted back to secondary, the flaps will still operate in the Primary mode. Look at the Slats Primary Fail Checklist, Note: Plan more time for slower slat operation. No mention of slower flap operation!
Flaps Primary Fail checklist also has a note: Plan more time for slower flap operation.
The asymmetry is sensed by the Left Inboard, Left Outboard, Right Inboard and Right Outboard sensors of the respective system, this detects the asymmetry between the left and right flaps or slats, not as you say an asymmetry between the flaps and slats.
