At the north part of "Lowlands: Troglodyte Lair - Spring," the entrance to the part of the cave...being the giant head in the picture, makes it impossible for me to proceed. Could this be cause I am taller than other PCs?

Yes the transition works, and it worked for me in Balor shape and Gold Dragon shape. Not sure what the issue was for you.

Send me a PM if it's still not working.