MouseOver Object overlaps fixed Object

[ich]

Hello,
I tried various options to solve my issue, but was not successful.

The set-up:
I have a nav bar which is a fixed object. Further down on the side I have several objects (e.g.pictures) with an mouse-over animation (mouse over appears Text and backgroundcolor over the picture)
Issue: When the mouse-over object is activated (= cursor is on the mouse-over object so that this level appears) then the mouse-over object is always on-top of the fixed nav-bar.
Target: Like the mouse-off picture, also the mouse-over object should "walk" beneath the fixed nav-bar when scrolling down.

Not so easy to explain I guess, this is why I did attach a picture, hoping it helps to understand.
Szenario1 = Mouse-Off
Szenarion2 = Mouse-Over

Regards,
HK