Banging the cervix shouldn't occur unless she hasn't had time to completely expand and her cervix tilt out of the way. It may still get rubbed on or bumped, but not collided with. It's the collision that many women find too painful. However, there are some women whose cervix are set at an improper angle and even when tilted their cervix can be hit, especially in some positions.
The anterior fornix was mentioned. It's closer to the opening than the cervix and doen't even require a long penis to reach and rub in the vast majority of women. It's quite possible the g spot and anterior fornix are getting mixed up when women and guys talk about the g spot. Some sex experts claim there is no such area as the g spot. Perhaps it's sensation from rubbing near or on the anterior fornix. This remains unclear.
The posterior fornix is deeper than the cervix. It's very close to the bottom wall. The deep area sensation that some women mention may be the posterior fornix being rubbed on.
The cul de sac, medically known as The Pouch of Douglas, is located between the bottom vaginal wall and anus. Therefore it is the deepest area to reach, and requires her to be elasticated and for him to have a penis long enough to push her bottom vaginal wall well into it. The deep area sensation that some women mention may be the cul de sac being contacted. Some believe that the cul de sac creates the most powerful sensation of all areas.
Many women require about 20 minutes of arousal before they become fully elasticated, fully expanded, and their cervix fully tilted. Articles saying that size doesn't matter tend to state that the disadvantage of a long penis is that it is prone to hit the cervix. Not so, as even an average penis can reach the cervix in most women if they are not fully expanded and tilted. And if they are fully expanded and tilted then a long penis will slide by it (unless she has a cervix that isn't set correctly, which a small percentage of women have). So long penises are getting a bad rap in 'feel good about your average size' articles. The main disadvantage to a long penis is if she isn't well elasticated then he can hit her bottom wall with too much impact if he forces it. Also, in cases in which he happens to be very long it is possible to push an elasticated bottom wall backward to it's ultimate limit and that can create too much pain in most women with an average depth vagina.