I have no idea when this happened, if it happened with iOS 11, 12 or 13, but I have noticed that iPadOS is NOT reported the correct internal amounts.
The amount of available, practical, usable storage is based not only on how much iOS/iPadOS takes up but on the actual size that 1.0 GB is equivalent to, which for Apple 1.0 GB=1.074 GBs
Also, iOS/iPadOS devices need to maintain a minimum constant of between 2-4 GBs to ensure nominal, expected performance and function of iOS/iPadOS.
Also, my installation of iPadOS 13, currently, takes up 5.2 GBs of my storage
So,
A 32 GBs storage iPad starts out with 29.8 GBs. Minus 5.2 GBs for iOS leaves. 25.6. Minus 3 GBs for iOS iPadOS system reserve equals 22.6 GBs of usable data storage space.
A 64 GBs storage iPad starts out with 59.6 GBs. Minus 5.2 GBs for iOS leaves 54.4. Minus 3 GBs for iOS iPadOS system reserve equals 51.1 GBs of usable data storage space.
A 128 GBs storage iPad starts out with 119.2 GBs. Minus 5.2 GBs for iOS leaves 114 GBs. Minus 3 GBs for iOS iPadOS system reserve equals 111 GBs of usable data storage space.
256 GBs storage iPad starts out with 238.4 GBs. Minus 5.2 GBs for iOS leaves 233.2 GBs. Minus 3 GBs for iOS iPadOS system reserve equals 230.2 GBs of usable data storage space.
512 GBs storage iPad starts out with 476.7 GBs. Minus 5.2 GBs for iOS leaves 471.5 GBs. Minus 3 GBs for iOS iPadOS system reserve equals 468.5 GBs of usable data storage space.
1.0 TB storage iPad starts out with 931.1 GBs. Minus 5.2 GBs for iOS leaves 925.9 GBs. Minus 3 GBs for iOS iPadOS system reserve equals 922.9 GBs of usable data storage space.
Currently, my iPad under iPadOS 13, reports, including with the system, I have used up 86.5 GBs of internal data storage for a leftover amount stated as 169.5 GBs on my 256 GBs iPad Pro.
This is incorrect.
After initial formatting, my 256 GBs iPad should begin with approx. 238.5 GBs of actual storage space.
After subtracting 86.5 I am really/actually left with 152 GBs and NOT nearly 170 GBs!
That is an 18 GBs difference is reported internal storage space.
I have no idea when this discrepancy in calculation of internal iOS device storage happened, but clearly users are being told by the iOS/iPadOS system they have more internal storage than the device actually has.