It would be helpful if you post a video while the printer is printing. A copy of your configh.h will also help.
Anyway, since it is a 3DR, using printed parts, problems related to geometric of the printer are the last I would look after.
All my "flatness" issues were related to the bed surface flatness, leveling of the bed, rods length (firmware and physical), joints and the reflector.
For example if you change the original reflector and take the mini kossel reflector....you will have a flatness problem because in this case the rods of one arm will not be parallel to each other. If you change the reflector, you must change the carriage, so that the rods stay parralel to each other. If not, you get something like the above picture. In the middle ok but the far you go from the center the worse it becomes, specially in that zone between Tower X and Tower Y.
Update: if you make the video, please do not acivate the two fans you have installed at the bottom of the printer. When I look to the picture avove, I think that the fans are blowing the PLA away from the print surface before it lands on the surface of the bed.
Anyway, since it is a 3DR, using printed parts, problems related to geometric of the printer are the last I would look after.
All my "flatness" issues were related to the bed surface flatness, leveling of the bed, rods length (firmware and physical), joints and the reflector.
For example if you change the original reflector and take the mini kossel reflector....you will have a flatness problem because in this case the rods of one arm will not be parallel to each other. If you change the reflector, you must change the carriage, so that the rods stay parralel to each other. If not, you get something like the above picture. In the middle ok but the far you go from the center the worse it becomes, specially in that zone between Tower X and Tower Y.
Update: if you make the video, please do not acivate the two fans you have installed at the bottom of the printer. When I look to the picture avove, I think that the fans are blowing the PLA away from the print surface before it lands on the surface of the bed.