Thank you all for your input!
Tenner, due to your warning (thank you) I have restructured my flights for an additional 35 Euro:
CDG-OSL (A-fare; 842 @ 200% - 1684)
OSL-ARN (A-fare; Min. 1200 - 1200)
ARN-CDG (O-fare; 925 @ 100% - 925)
Total miles = 3809
Pretty unfair of SK/A3 to skim miles like that, anyway all booked now!!
Now I'm trying to cancel my original A-fare SK ticket from CDG-ARN with difficulty (will not let me do so online!)
Cheers again FTers!