Happy Thanksgiving! It might be a good idea to double check the formula:
((R49<8)+R50)/100 . A missing or misplaced parenthesis could really screw things up.
R49*2.56 + R50/100 should also work.
Except for the numbers, the behavior you describe sounds similar to what I see:
Constant readout during a regeneration and for a while (50 miles for me) afterwards, then a jump to a lower number (usually 6 to 8 gram for me - haven't checked it that often) and slow increase from there.
The erratic jumps also point in the direction of a wrong math formula, or that your car's computer has gone bonkers. Maybe VW tried a special improved cheating firmware in yours...