First of all, get out a really worn deck. This'll make it far easier at first.
Right then. It looks like your pivot point is wrong. It looks as if it's too close to the left, too close to the heel of your thumb. This is a tendency with the pressure fan: this grip allows for the strongest grip but compromises on range.
To show you what I mean, try this little experiment:
Take two cards and hold them in your normal, pre-fan position. I'm assuming from your pictures that you are fannng in your left hand. If not, just reverse the 'lefts' and 'rights':
Firstly, place you thumb in the leftmost position, so that the pivot point is tucked up against the heel of your thumb.
Try and rotate the top card around 180 degrees so that it is pointing the opposite direction. Notice how much range of movement you get between the two cards.
I get about 100 degrees before the card jams agains my hand. Certainly less than the 180 degrees minimum that you really need.
Now then. Start this again with the two cards, but move the thumb to rightmost edge, so that your pivot point is as far away from the heel of your thumb as possible. Rotate the top card downwards.
You should be able to get more range of movement. I get about 200 degrees.
Can you see how the range of the fan is limited by the pivot point?
The problem with this second pivot point is that it is too far away from the heel of the thumb, and this tends to make the grip weaker. For a good pressure fan, you need a strong grip.
Your ideal pivot point should therefore be somewhere between the two. A compromise, really. I have mine almost bang in the middle. There is a test for the pivot point being bang in the middle: When you rotate the top of the two cards 180 degrees, they should be bang in line - not jogged to the left or right.
If you play with your pivot point, you will find a good compromise. I would start by moving it outwards in little increments.
Don't be afraid to use a fair amount pressure! That is of course why you need a strong grip. Like I say, try using a really tired and worn deck... They'll be easier to bend backwards.
Oh aye, your thumb fan looks spot on. It shouldn't take too long to get your pressure fan right.
Hope this helps!
Mark.
