WeeFoal is right. Dystocias can be much more common in minis. There is not as much room in a mini mare for the foal to get positioned correctly.
Most serious breeders have TV cam coverage and foal alams/foal alerts and systems for monitoring so they can be there at foaling time.
The sac around the mini foal seems to be thicker in proportion and many times a foal cannot get out unless you break the sac.
And yes, there is so little room inside, it is quite difficult to get your hand or arm in to reposition a foal if you have to do that.