This harness is a to small for Sunflower. It is a horse size, and Sunflower is 15.3 and 1500#.
While it is adjusted properly, it just looks small. It looks much smaller with a photo of the entire horse. Also it is adjusted all the way out, on the last hole. You should try not to use harness on the last holes because it gives you no adjustment leway, If the harness breaks there is no extra leather to use to repair or even to get you back home.
Now I am not going to say you can't use the last hole, but I am saying if possible don't, Get a bigger harness.
First two photos are of the horse size harness.
Second two photos are of an XL horse harness. You can see it is much more substancial in size and is not on the last hole of the buckles.