Problem - shrink-wrapped boundaries (+ region union command)

Hello everyone,

In my simulations, I am using the union command to obtain a cubical region as region domain and, subsequently a cubical simulation box:
In my code I have the following regions(s):

region POROUSMEDIA_BUMPYWALL block 0.0 0.6 0.0 0.6 -0.05 0.0 units box
region porouscenter block 0.0 0.6 0.0 0.6 0.0 0.2 units box
region porous1 block 0.0 0.12 0.0 0.6 0.2 0.3 units box
region porous2 block 0.12 0.24 0.0 0.6 0.2 0.3 units box
region porous3 block 0.24 0.36 0.0 0.6 0.2 0.3 units box
region porous4 block 0.36 0.48 0.0 0.6 0.2 0.3 units box
region porous5 block 0.48 0.6 0.0 0.6 0.2 0.3 units box
region CR1 block 0.0 0.12 0.0 0.6 0.3 0.4 units box
region CR2 block 0.12 0.24 0.0 0.6 0.3 0.4 units box
region CR3 block 0.24 0.36 0.0 0.6 0.3 0.4 units box
region CR4 block 0.36 0.48 0.0 0.6 0.3 0.4 units box
region CR5 block 0.48 0.6 0.0 0.6 0.3 0.4 units box
region CRcenter block 0.0 0.6 0.0 0.6 0.4 0.6 units box
region POROUSMEDIA_LAYER union 6 porouscenter porous1 porous2 porous3 porous4 porous5 units box
region CAPROCK_LAYER union 6 CR1 CR2 CR3 CR4 CR5 CRcenter units box
region CAPROCK_BUMPYWALL block 0.0 0.6 0.0 0.6 0.6 0.65 units box
region REV union 2 POROUSMEDIA_LAYER CAPROCK_LAYER units box
region SYSTEM union 4 POROUSMEDIA_BUMPYWALL POROUSMEDIA_LAYER CAPROCK_LAYER CAPROCK_BUMPYWALL units box
create_box 2 SYSTEM

and they work with

boundary pp pp pp

but I need

boundary pp pp ss

So when I use the second boundary command, I receive an error "Illegal simulation box".

I have reviewed the commands, regions, create_box and boundary and, I don't see any restriction between union-shrinkwrapping and periodicboundaries-shrinkwrapping, so I don't get what I might do wrong.

Any suggestion?

Cheers,
Luca

### Ver 3.3.0