Sergio:
Your English is fine. Much better than my French, German, Italian, and the list goes on.
I understand what you are saying. The piece is blown using a mould for at least part of the process. The blowing can continue after the piece is removed from the mould, and often there is more expansion at the top of the glass. So, the section at the top could have bigger protrusions/knobbles than the section at the bottom.
David