Prohibition ended just before scientific polling took off in the U.S., so we don't have high-quality polls from the 1920s. What we do have are polls of specific magazines' readers. Now, keep in mind that bias enters these numbers twice: magazine readership is not representative of the population, nor are those who respond to magazine polls representative of magazine readership. Nonetheless, the results from the Literary Digest Prohibition Polls are at this link.

  To summarize these polls: In the 1920s, straight enforcement was not a majority opinion among respondents, but neither was repeal. Initially, 40% of respondents wanted to modify prohibition somehow, which seems consistent with OP's research that people did not entirely understand/approve of the details of prohibition. Nonetheless, public opinion seems to have consistently moved toward "repeal" with the passage of time. By 1932, 74% of respondents indicated they were for repeal -- and in fact, this percentage matches perfectly with the official vote on repeal in the 39 states that put prohibition up for a vote after the repeal of national prohibition.

The earliest scientific poll I could find on prohibition comes from Gallup in December 1936. In it, 67% of respondents indicated "no" to the question, "If the question of national prohibition should come up again, would you vote to make the country dry?."

(Source: USGALLUP.DC2036.R01; sample size around 1,500)

Prohibition ended just before scientific polling took off in the U.S., so we don't have high-quality polls from the 1920s. What we do have are polls of magazine readers.*

The results from the Literary Digest Prohibition Polls are at this link. To summarize them:

• In the 1920s, straight enforcement was not a majority opinion among respondents, but neither was repeal. Initially, 40% of respondents wanted to modify prohibition somehow, which seems consistent with OP's research that people did not entirely understand/approve of the details of prohibition.
• Public opinion seems to have consistently moved toward "repeal" with time. By 1932, 74% of respondents indicated they were for repeal--and in fact, this percentage matches perfectly with the official vote on repeal in the 39 states that put prohibition up for a vote after the repeal of national prohibition.

The earliest scientific poll I could find on prohibition comes from Gallup in December 1936. In it, 67% of respondents answered "no" to the question, "If the question of national prohibition should come up again, would you vote to make the country dry?"

* Keep in mind that bias enters these numbers twice: magazine readership is not representative of the population, nor are those who respond to magazine polls representative of magazine readership. But in this case, they actually might have been fairly accurate (see the second bullet point).

Citation for Gallup Poll: USGALLUP.DC2036.R01; sample size around 1,500. I can't provide a direct link because I found it at the Roper Center's Public Opinion Archives, which is a password-protected database.