Strange behaviors in the "position property"

[Luigi]

I would know what "criteria" is used in box positioning with the
position property.

Here my tries (using IE and Opera):

I have a box with an absolute positioning (properties used: position,
left and top).

I noted that if the reference of this box is the "html" box or the
"body" box, the browser uses the following rules:

distances between the "container box" and the "positioned box"
borders:

* vertical= "inner box" margin + top;
* horizontal= "inner box" margin + left;

If the reference of the positioned box is another box (defined with
the position: relative property), I have these results:

* horizontal= container padding + "inner box" margin + left;
* vertical= "inner box" margin + top - container "upper border";

All this using IE. With Opera I have this situation:

* horizontal= "inner box" margin + left - container "left border";
* vertical= "inner box" margin + top - container "upper border";
PS: All these boxes (including the "body" and the "html" boxes) have
positive paddings, margins and borders.

I think this is a very incoherent behavior!

Must I accept that? (using the position property in an approximate
mode ...)

Or it is a better thing not to use the position property at all.

Or I'm failing something in style sheets use.

Can you help me?
Thank you. Luigi.