I think that is normal. Attached is a pic of when I did mine. I had a short piece of aluminum I used to measure the distance from the face to the studs to get an idea if how many shims to use on each one.
You can see there is a gap from the tub to the face that is pretty large.
I would also recommend the reinforcement plate while it's apart. I bet 75% of the lower studs crack at the pan.
