Hi Sergi!
My account is still alive for your site, so I can see the settings.
I saw that there is no common category set between products and portfolio items, and you do not use manual relationships. One of them would be preferred to increase relatedness between these elements.
For example on “Related Types” (Tipos relacionados) tab of WRI Settings page “Product Categories” can be set in Related portfolio (Relacionado Portfolio) section.
If you do this, an extra categorization metabox will be displayed on Portfolio edit pages, so portfolio items can be classified into product category. So the products in the same product category will be similar to this portfolio item.
Alternatively you can use the opposite solution, so you can use portfolio categories for products, or you can use the special Similarity Marker Categories, if you set “Enable Similarity Marker Categories (pro)” checkbox (Habilitar Categorías de Similarity Marker).
In these cases you will also get extra categories on product and portfolio edit pages, so you can and you should adjust related portfolio items and portfolio elements to the same categories.
So the key is, that you should decide how would you like make connection between the different elements (using common category system or apply similar title/content or manual relationships or the combination of them)
On the other hand, please decrease the “Match threshold” (Umbral de coincidencia) on “Product page” tab of WRI settings page, because if the threshold is too high, then you will not get any similar items.
I hope this information is useful for you.
Peter