In designer or architect, all our processes are horizontally.
When we publish the repository, the situation is as follows :
The model in first tab called "Model view" is horizontally (from left to right), and that is how it first appears in the publisher - However, the other views, automatically generated, (useful elements); (simplified process or simplified view); (complete process) are all displayed vertically (from top to bottom).
Moreover, in complete process or simplified process views, junctions between activites are overlaping on other activity.
I was not expecting the portal to automatically change the orientation from horizontal to vertical... can this configuration be altered through some parameter settings or change the config files ?
It depends on the amount and kind of customizing which has been applied to your set up. Assuming there is no customizing at all you may take an ARIS Business Architect setting into account: View, options, layout.
During export such settings are transported to ARIS Business Publisher. The ARIS EPC layout strategy defaults to vertical. Changing might solve your problem.