The idea behind the point system. For a full grade upgrade (from 4 to 5 or 7a to 7b), the points of the lower grade are multiplied by 1.75. For example: a "5" gives 21 points. The next full grade is 6a which gives 38 points (21 * 1.75).

Any minor upgrade/downgrade (from 5 to 5- or from 6a to 6a+) adds/subtracts 33% of difference of 2 full grades. For example: the difference from a "7c" (615 points) to an 8a (1078 points) is 463 points multiplied by 0,33 gives 153 points -- added to the "7c" results in 768 points for a "7c+"

I also tried a different factor: "2" for a full grade upgrade but the numbers get crazy big then.

New Approach

Using y = 4^x

Which translate to 4 times more points for a full grade upgrade. Or concretely spoken, you need to ascend a 6a 4 times in order to get the same points as 'cending a single 7a.

For the distribution of the minor grade upgrades (from 7a to 7a+) we use the tangent at the full grade point to calculate the points. It makes the minor upgrades gain less points compared to the graph of 4^x.

PHP code demoing the idea

for( $x = 0; $x <= 8; $x++ ) // grades from 1 to 9 (zero based index)
{
  $y = pow( 4, $x );
  echo "\n";
  echo "Point: ($x,$y)\n";

  for( $x1 = 0.2; $x1 <= 1; $x1 += 0.2 ) // minor upgrades (7a to 7a+)
  {
    $x1i = $x + $x1;

    $m = log(4) * pow( 4, $x );
    $n = $y - $m * $x;

    $y1i = round( $m * $x1i + $n );

    echo "Point: ($x1i,$y1i)\n";
  }
}