I don't know the exact ratio. It takes about 50 HP to get a curation reward of 0.001 . Accounts with under 50 HP rarely get rewards. It is silly to tell new users with between 0 and 25 HP about curation rewards, because they won't be seeing curation rewards.
Small accounts only get curation rewards if they front run large upvotes. Even then the curation reward is tiny.
Just go into the wallets of new accounts that did not buy HP. They usually have no curation rewards.
I think it is best to bring up the question of curation rewards under the banner of why new users should buy HIVE POWER.