I play a low D Howard and Sweatheart and have short small fingers.
If I try to play normal or pipers grip i get cramped wrists and a sore thumb. So i use my little fingers to cover the third and sixth holes and my ring fingers to stabalise the whistle, (takes a little while to get used to it and can be confusing to change back to playing the high whistles but very comfortable). Its sort of a semi pipers grip but use the end pads of little fingers and 2nd pads of first two fingers. I can now play for hours with no pain or cramping. Can leave ring fingers down permenantly or take them off of the same time as little fingers so as you dont have to re-learn fingering so much.
Totally agree with other replys re pain - your body’s way of saying stop.
Goodluck