I'm at least passingly familiar with the 20th-century reforms (the Parliament Acts 1911 and 1949, plus the reduction in the number of hereditary peers during the Blair government) that reduced the power of the Lords during that period. But clearly by 1911 the Commons was already the "main" house, in that for example there was no question whether a Liberal could be Prime Minister when the Conservatives controlled the other house.
So when did the change happen? Is there a specific vote or issue that can be pointed to as the first time that the two houses disagreed and the Commons prevailed? Were there politicians (on either side) particularly associated with that transfer of power?
In my opinion you answered your own question. It probably was the Parliament Act of 1911 and the People's Budget that allowed the Commons to become pre-eminent. Convention during the 19th had led to it becoming more common for the Prime Minister to sit in the Commons but right at the end of the 19th century both Earl Rosebury and the Marquess of Salisbury were prime ministers despite sitting in the Lords.