I hate to say it 2C but you are wrong about diluent being a part of the operating cost.

Diluent cost is subtracted from the gross revenues and the presented as a production revenues.

Q2 example : (WTI oil $120)

Gross bitumen revenues.....$85 M

Diluent purchased...............-($39 M)

Transportation and marketing cost.....-($3.4 M)

Net bitumen production revenue...........$42 M =$61/bbl

Royalties ..............-($0.5M)

Operating cost.........................-($20M) = $29/bbl

Total netback......................... $ 22M = $$31/bbl

As you can see the diluent has no part of the operating cost. The SOR is the main parameter effecting the OP cost.

When you subtract Financial charges and administrative cost of $21/bbl you have $10/bbl free cash flow. This is at WTI $120/bbl.

WTI $100 to $105 is the brake even point.