try to use the OriginalViewpoint to let them Centered for all Display Sizes, like 1920x1080 and 1280x720 and so on.
just add for example + 200 on X or Y after
for X: OriginalViewpointWidth / 2
for Y: OriginalViewpointHeight / 2
for X: OriginalViewpointWidth / 2 + 300
to get your position u want it to be.
Edit: it means it takes the current Viewpoint Size and devide it by 2 = center the Object on screen, than u can move it with +/- for what position u want