Hello all,
I played for some time but maybe some mechanic is eluding me. 
Most of the position variations cannot be selected. i.e. doggy.
Are they placeholders or I need to do something to make them available?

I think you need to buy the full version of it...

Not all positions are available currently, and unlocking is not functional. 

I think only cowgirl and from behind have sub positions, the others do not currently.