Hi guys

I'm having a great problem with the positioning of sprites. I want to do a lot of animated stuff in the background of my menus, but I am stuck at a very fundamental issue and can't solve the problem.
Let's assume my screen resolution is at 1920x1080 and I designed graphics for that "full screen"-resolution. Although the single moving objects might be smaller, they are designed to fit at a certain related position on that full screen-display.
To speed up things; everything works perfect when setting the .graphicsDevice.Viewport/BackBuffer/ect.-stuff to "my full screen".

However most of the time I am running my programs in a #defined "Debug-Mode" where the screen resolution is set to 1280x720. - And there is the problem: Nothing is how it's supposed to be!

By now I already solved one big part of the problem - the rescaling of the sprites! I just created a TextureScaleMatrix and used it as an argument in the SpriteBatch.Draw()-Calls...
now all the images are scaled correctly and have there intentional proportions on any resolution. - Great! BUT....

scaling the images alone doesn't work, because they have to be drawn at certain positions too!!! - That's where I am stuck. For now it seems to me, that there is absolutely no way of scaling the positions like I did with the images.
I tried using the matrix, using single float values for resolution-relations... and so on...
Although sometimes I got almost where I wanted to, it still wasn't good enough, because (i guess) some coma values simply get lost when calculating around the screen.
But even more frustrating; most of the times the results are simply unbelievable and completely incomprehensive.

Like I said, scaling and drawing the objects themselves within original proportions is not a problem using a Matrix, but what about the positions they need to be drawn?
Do I have to create a raster that is logically structured in ... let's say 1/3 of the screen, 2/3 of the screen, half the screen, and so on... that seems not to be flexible enough for my purposes, and the smaller the scope the more inaccurate it will become yet again.

Maybe all of this scaling is not neccessary the begin with? I have no clue how an xbox will handle that depending on the television it's running on.
Can I just say like "ok, I want to create everything in 1920x1080 and it will no influence the program while being fine/scaled to fit on any television out there, even if it is 4:3"?