[Question] Why are the distances between the grade thresholds irregular?

I noted yesterday, that the point thresholds for reaching the grades 4.0, 3.7, …, 1.3, 1.0 are not evenly spaced. For example, if 100% maps to 70 points and the 4.0 threshold is at 35 points, exapje calculates these thresholds:

Exapje threshold:
[35.0 37.0 41.0 45.0 49.0 53.0 56.5 60.5 64.5 68.5]
Differences:
[2.0 4.0 4.0 4.0 4.0 3.5 4.0 4.0 4.0]
Corresponding percentages:
[50.0 52.9 58.6 64.3 70.0 75.7 80.7 86.4 92.1 97.9]

Note, that it is very hard to reach the 1.0 (98% are required). The situation is even more odd, if the passing threshold is lowered from 35 to 34 (probably because more rounding is applied):

Exapje threshold:
[34.0 36.5 40.0 44.5 48.0 52.5 56.0 60.5 64.0 68.5]
Differences:
[2.5 3.5 4.5 3.5 4.5 3.5 4.5 3.5 4.5]
Corresponding percentages:
[48.6 52.1 57.1 63.6 68.6 75.0 80.0 86.4 91.4 97.9]

Why is that?

I would have expected, that the distances roughly match steps of 5% of the total points, or are at least roughly equal. Something like this:

##### Scenario of passing_threshold=35.0, full=70.0 #####
5% of total points equals 3.5 points (reference)
Thresholds without rounding:
[35.0 38.5 42.0 45.5 49.0 52.5 56.0 59.5 63.0 66.5]
Differences:
[3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5]
Corresponding percentages:
[50.0 55.0 60.0 65.0 70.0 75.0 80.0 85.0 90.0 95.0]

Thresholds rounded down:
[35.0 38.0 42.0 45.0 49.0 52.0 56.0 59.0 63.0 66.0]
Differences:
[3.0 4.0 3.0 4.0 3.0 4.0 3.0 4.0 3.0]
Corresponding percentages:
[50.0 54.3 60.0 64.3 70.0 74.3 80.0 84.3 90.0 94.3]

Thresholds rounded to 0.5:
[35.0 38.5 42.0 45.5 49.0 52.5 56.0 59.5 63.0 66.5]
Differences:
[3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5]
Corresponding percentages:
[50.0 55.0 60.0 65.0 70.0 75.0 80.0 85.0 90.0 95.0]

##### Scenario of passing_threshold=34.0, full=70.0 #####
5% of total points equals 3.5 points (reference)
Thresholds without rounding:
[34.0 37.6 41.2 44.8 48.4 52.0 55.6 59.2 62.8 66.4]
Differences:
[3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6]
Corresponding percentages:
[48.6 53.7 58.9 64.0 69.1 74.3 79.4 84.6 89.7 94.9]

Thresholds rounded down:
[34.0 37.0 41.0 44.0 48.0 52.0 55.0 59.0 62.0 66.0]
Differences:
[3.0 4.0 3.0 4.0 4.0 3.0 4.0 3.0 4.0]
Corresponding percentages:
[48.6 52.9 58.6 62.9 68.6 74.3 78.6 84.3 88.6 94.3]

Thresholds rounded to 0.5:
[34.0 37.5 41.0 45.0 48.5 52.0 55.5 59.0 63.0 66.5]
Differences:
[3.5 3.5 4.0 3.5 3.5 3.5 3.5 4.0 3.5]
Corresponding percentages:
[48.6 53.6 58.6 64.3 69.3 74.3 79.3 84.3 90.0 95.0]