Thank you but, Nope

This would be easy
I need ONE box fitted to the Bounding size of Clipped splines. Ideally would be like the picture example.
The final generator is for generating doors/windows etc. and I`ll have to adapt to the client workflow.
I`ll get prepared two sets of splines:
- Base/horizontal >> to get width/depth (X fixed | Y fixed size
- Vertical >> to get width/height (X fixed | Z fixed size)
So, I`m missing either Y | Z fixed size.
Also, one of the splines will be marked with a specific ID which will determine the type of Geometry (Door type, Normal window, Sliding window, etc)
I know I can use various RC features to accomplish all those tasks and I have prepared a lot of SubMacros to make it automate as much as I can.
The only small issue is this topic problem

.
How to extract third dimension value from the "opposite" clipping SubSpline and then use it in common Style and common Generator.
P.S.
Since all those splines are generated by a script I have a workaround solution:
- one SubSpline will carry ID for the Geometry type
- second SubSpline will carry ID equal to my missing dimension (Y | Z depending on the Style)
But for this, I have to change the Script and this is probably out of my range.