To detect an imagetarget well, we need to assure that the imgaetarget is as large as enough in the camera view, typically no less than 30% of the whole image size. The smaller the target looks in the camera the harder the detection goes.
For your case, ~70cm*60cm image is physically large indeed but is much smaller than expected considering with your shooting distance. So enlarge your physical image could help.
By the way, better hardware device won't help the detection itself but can improve the detecting speed.