Insisting on and checking a paper fuel plan seems to me to be a pretty pointless regulatory exercise.
If they won't believe what I say, why would they believe what I write?
A properly set up I0520 can cruise happily at 42 litres an hour or 62 litres an hour, but not in the middle, with only a few knots or so difference in TAS. A properly set up and run I0520 will eat far more fuel in an ROP climb than an I0520 that's being beaten to death at 25/25. Same laws of physics and systems characteristics drive the same outcomes on many other piston engines.
How on earth would the neddie from CASA know whether the numbers in a paper or mental fuel plan bear any semblance to reality or, more importantly, are safe? If it's just that paper fuel on board is greater than paper fuel calculated as required plus reserve, it's a pretty pointless exercise.