Core One preassembled: Print bed doesn't reach temperature, uneven temps across the bed
I have had a lot of trouble with bed adhesion since I moved to the Core One (pre-assembled). Even with PETG, and that was so sticky on my old MK3S+ that I had to do something to make it worse or it would pull the coating off t
he print sheet. It was especially bad when printing large parts that covered the whole bed - the front right and bottom left corners were lifting off.
Asked around and someone suggested to raise the bed temperature by 5°C, so I did and it solved my immediate problem. But I also raised the chamber temperature by 5°C (which mostly turns the cooling fans off, so less draft I guess) and increased my first layer height to 0.25 mm from 0.2 mm.
I also ordered an infrared heat measurement "gun" and used it to measure temperatures at different spots of the bed during a print. The attached pictures show the print bed temperatures with the nominal set to 90°C. I am reaching 85 in one spot, in other spots it is barely 82 and especially around the edges it drops off a lot (to be expected if you know where the heated part ends, but still).
Is this normal? Where is the temperature of the bed measured by the controller? I feel like I should not have to set the bed temperature to 90°C to achieve 8° less than that in most places. And I never had this issue on my MK3S+ (in an enclosure). I should also be able to use the whole print area to print (with no space for a brim unfortunately).
I should add that this was measured during the "absorbing heat" phase, but while printing it does not become better.
