First of all, penetrating the cervix is physically impossible. If it did really happen it would be a medical emergency.
Clitoral orgasms can be achieved with almost any stimulation (a penis isn't necessary), and vaginal orgasm can be achieved with an average sized penis/ dildo, although several studies have indicated that it is easier for a woman to orgasm with a longer than average penis. Add to that that most women actually consider girth more important than length.
Finally, whilst size may or may not matter depending on the girl (in most cases it does, like it or not), to achieve cervical orgasm the penis does need to be significantly larger than average. Simple physics.
To achieve cervical orgasm, the boyfriend, or bull, or bulls
, will need to introduce their penis/ penises very slowly and gradually into her vagina. If there are bulls, she probably won't need the boyfriend's/ husband's dick. When the head of the penis feels resistance, refrain from hard pushing, move gently and try to "massage" the cervix (it feels like a really small donut). If done correctly, the girl will feel a very strong orgasm that lasts longer and is more "full bodied" than a clitoral or vaginal orgasm.
I would say that this is the point where you can experiment with going a bit harder but I think you'll find that most girls like it hard about 80% deep but a little more gentle when it's 100% in, assuming we're talking about black penises on the larger size.
My ex had multiple bulls but her two favourites were both absolutely enormous... We used to call her other bulls BBCs and these two XtraBBCS.
Porn makes everyone think that girls like it when Mandingo forces his cock into the girl right away and just hammers her into the wall bit in reality of she is working with dicks around that size (and these two were), it takes patience and a fair bit of time of time to gradually get that thing in there.
But yeah, when it's in, she is in ******* and much like a lot of the comments here, when the head of his penis is against her cervix, she often experienced a very very strong orgasm at the point when he ejaculated, like the throbbing and vibrating of his penis caused her to let go.
I usually came not long after too.