Correct, it really depends on the pool that you are using on how they do visualize the mining stats and i didnt even see about that flat line, maybe its just an another setting of the chart that you mean. Zig-zag would be always noticeable and its a good indication and besides mining difficulty does increase which means hashes or profits would be more lesser and lesser.
The problem is we are using the same pool, the same bios. and also tried the same settings. but with his setting my rig is going offline even rig restarts every 20-23 minutes.