Where was he hitting with his penis in those positions you mentioned? The usual solution to make yourself lower is to spread your legs apart while standing, kind of like the "horse stance" in martial arts.
What I've heard from horse zoos is taking a stallion where your body is horizontal to the floor and his penis enters parallel to your spine is dangerous because he would have nothing but organs stopping him from going balls deep. Doggy style and mounting with stallions is high risk. They recommended taking horses standing up so when his penis enters horizontal to your vertical body he will hit your pelvis and stop. Also they suggested taking stallions off to the side so his thrusts are not as powerful.
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