Countered my return offer using level data even though it felt risky as a new grad

Got the return offer email, base was fine but the sign-on was way below what I'd seen posted for the same level at the same company. Spent an evening pulling comp data and wrote one email, three sentences, just stating the number I'd seen and asking if there was flexibility. Almost didn't send it, kept thinking they'd rescind the whole thing over a new grad asking for more. Recruiter came back within two days with an extra $6k sign-on, no pushback, no drama. Wish I'd known asking as a first offer doesn't automatically read as ungrateful.