I'm on board with Bob's reply, I always figured 5 to 6 ft down with most of the line out. They also sell a super sink that about doubles that which works well as the water warms or the sun gets higher
ya a friend just got a spool think it was 92.00 at ktp its hard to find the Cortland 333 level sinking line
Cortland Sinking Salmon level line 6WT. Been using it for over 40 years. I've heard AJ's Bait&Tackle, FishUSA has it for sale...?? Been working for us!!!