Marital relations

As you know, option C is very painful for the opponent, and impossible during normal life.
But in pregnancy it is okay.
Naturally, this is how the Creator designed it.

But of course you have to ask permission before and be careful not to hurt
If it hurts, quit

Do you think this is permissible only in the above circumstances, or also in general, when she is not pregnant?

What emerges from the sources is that the entrance should be with the husband on top. At least some of the things that are based on health considerations should be discussed as to whether they are mandatory, and even modesty considerations may change over time. But there is no room here to elaborate.