I think it is better to work with 88es calculated wellhead...

I think it is better to work with 88es calculated wellhead pressure of 3500 psi. The 5200 psi at 4000 ft is virgin data recorded prior to disturbing the well with operating procedure's. It aligns quite well with 2700 ft of frack water and 1300 feet of diesel.
2700 ft frack water @ .44 psi/ft = 1188 psi
1300 ft diesel @ .39 psi/ft = 507 psi
1188 + 507 = 1695
take 1695 off 5200 gives wellhead of 3505 psi
You will notice the diesel psi/ft has been adjusted from the original .36. It has a range of .35 to .42 so .39 is still acceptable given we don't know which diesel has been used. 88E has the advantage of knowing all of the above so I trust their number.
The well head gauge is a different matter and looks like 2750 psi to me, we don't know exactly when it was read. I expect such an important gauge to be regularly tested and calibrated so believe the number pictured
You would expect, but don't know, after the down hole plug/valve separating the diesel from the frack fluid has been opened. So conditions have changed
Is there less diesel ?
Has a heavy fluid been introduced to the wellbore in the wire line operations or for other operational reasons. In short a lot of don't knows.
If the fluid above the 4000 ft mark was at .61 psi/ft perfect alignment with gauge
Back to the reservoir pressure working with the reliable data of 5200 psi at 4000 ft and using a frack fluid estimated at .44 psi/ft . There are another 7000 ft at .44 to add, (3080 psi)
5200 + 3080 =8280 psi in the reservoir.
Although it doesn't match the .82 psi/ft given by the company (9020 psi) I would be happier with a lower pressure due to the positive implication it has to Gas Oil Ratio
Wish I could give a more accurate number, but there is so much we don't know at 100% confidence