I was having trouble with PETG printing consistently, and found it worked a lot differently on different parts of the bed. We had an infrared cooking thermometer, and this worked really well to isolate the problem - I was able to see that when I set the bed to 85C, parts of the bed were at 108C (!). So this caused melting/warping in those areas. I see there are some plates for heat conduction, which might be a good solution. But I ended up solving the problem by just backing down the bed temperature after the first layer. No more issues. A couple example thermometers are: