How high are the home row keys relative to your elbows? (In other words, how high is your desk relative to your chair.) The proper tilt to use depends entirely on the angle of your arms.
Ideally, you want to be typing with your wrists as straight as possible (not extended, not flexed), and with your palms and wrists “floating” in the air, not resting on a palmrest (and definitely not resting on the table). My personal suggestion is to angle the keyboard such that the PCB/plate are parallel to your forearms when your wrists are straight and your fingers are resting on the home row.
Keep your keyboard relatively close to your body, so that you don’t have to reach your upper arms forward to reach it. Leave your upper arms hanging loosely down at your side, don’t let your elbows stick out sideways by more than 6 inches or so (maybe less), and keep your back straight and your shoulders relaxed, not shrugging upward or forward.
At that point, your posture should be relatively okay even if your keyboard is a few inches above your elbows, but the most comfortable position to put the keyboard is at the level of your elbows or a few inches below that (which takes either a low desk or an under-desk keyboard tray, or else a relatively tall chair with a forward-slanting seat or a tall stool or similar, or a standing desk). Regardless of the keyboard position, angle it such that the surface is parallel to your forearms as I mentioned before. At the most comfortable height, this means the top of the keyboard should be flat or even tilted slightly negative; to accomplish this, use a tilting under-desk keyboard tray, or pile things under the front side of the keyboard.
The keyboard tilt you are describing in your post sounds like it’s optimizing for a relatively low chair and a relatively tall desk.