Goran:
I have made exactly what you told me, and now everything seems to be aligned.
At the beginning, I took the wrong way. Let me explain it. My baseboard is a kitchen worktop put on three brackets on the wall, without any table legs. So, I started shimming this table. It was a bad idea, mainly because, after I shimmed the table, it was not completely horizontal and the easel did not settle appropriately on the table.
Then I read your comment, so I came back to the original situation, with the table perfectly levelled. Then, I followed your suggestions and finally I got what I was looking for.
I want to thank you for your post. It was the only one, but it was the one I needed. This kind of things is a prove of the Apug fortress.
Thanks again,
Henry.