I could be wrong but given that the home position is set by the machine finding the minimum x and y distances, 0 is where the bot hits the end stop on each axis.
A plant that is placed at (200,200) isn’t 200mm from the physical edge of the bed but 200mm away from the home point plus the distance from the point of the tool carrier that hits the end stop to the UTM. If the UTM is offset from the part of the carrier that hits the end stop by say 100mm, a plant at (200, 200) would actually be 300mm away from the end stop if you measured it with a ruler.
If you move the bot to the location of a plant, it will be close to being in the centre. Might need to measure the distance from the UTM to the camera and build in an offset to your position. I found that when I took a photo of a particular plant, if it wasn’t in the centre and I tried to move the machine so that the camera was directly over the plant, the axis were messed up. It looked like I needed to move it in the x axis but it was actually the y axis that I needed to move it on.
Don’t know if I’m correct but that’s my understanding of it.