It's tough when a Tom is following a hen, try to duplicate
whatever the hen is saying except a little louder and cut
her off with your response whenever you can. If your
lucky and get her mad she will come to give you a
trouncing and bring the Tom with her.
Yes when a bird is coming from behind change positions
unless you think he will see you. I've even stood but before and
leaned against the tree because I couldn't move to the back
side of it.
Chasing is okay, just got to be careful not to get busted, it's
not easy and every good Turkey hunter has been busted
many times.
20 guage---first get a real turkey choke , second pattern
your shotgun to find the best shell for it, every gun has
a best shell for Turkey hunting---once you find it 40
yards should be doable.
Best of Luck!