thanks, all, for your fast replies!
yep. i believe it is flat, i also doubled checked that the door closes fully on both sides. my glass door is bowed/curved upwards as well, which i think is common, but i did not try to flatten it with weights.
i was thinking of getting these bar shaped ones from amazon: https://www.amazon.com/gp/product/B075N8ZZGB/
actually, the ruler did not cut exactly where it was positioned. for example. if i cut again starting from the misaligned image in my post, the 2nd cut would be exactly where the first cut is, but still not where i planned it to be. so, you’re right the cuts are repeatable, but both with the same offset errors from planned. i can apply the appropriate correction offsets (similar to A way to improve object placement) but the amounts would be slightly different across the bed. i think the 3rd picture from this post Alignment / Fisheye help illustrates the non uniformity.
i think the glowforge currently works really well for “direct-to-print” images, where we don’t have to position precisely. one of key advantages of glowforge for me is using the camera to align with the material being cut. i had a 50w “shenhui” laser way back when, manually setting the head height and positioning with the red laser dot is such a pain. this is light years ahead! i’m just abit surprised by the rather large offset errors, which i had thought can be (camera) calibrated. hence i wanted to check if this can be fixed by software or there is some other hardware/mechanical/alignment issue.