Warped TAZ-6 PLA print

I searched the forums and haven’t found anything addressing this precise issue.

When I make a long (distance, not time) print, there noticeable curvature of the print along its length. Essentially I am printing a 200mm x40mm x5mm bar. The curvature results in maybe about 1/2 to 1mm of gap between the print and a flat surface at the middle of the print. The CONCAVE side faces the bed. I am using Polymaker Polylite PLA, and standard settings on the temperatures/fans/etc. There is good bed adhesion, I usually have to gently pry the print off the PEI bed.

When I print the same thing, but 15mm thick, then the warping is less obvious, but still there. Smaller length prints don’t have as obvious a warp, but even 100mm lengths have some visible warp.