Nor were they reduced in proportion to...

For the provinces of Great Russia (Velikorossiia), for instance, the law established a scale of charges corresponding roughly to the division of that area into zones according to the size of the allotments.
There were four maximum annual charges of 12, 10, 9, and 8 rubles which were imposed on the holders of maximum allotments in the respective zones. These charges, however, did not reflect the market
value or the productivity of the land, nor were they reduced in proportion to the decline in the size of the allotments. In the industrial non- black-soil zone half of the total charge fell on the first dessiatine of
the allotment; one-fourth, on the second dessiatine; and the balance was equally assessed among the subsequent dessiatines. For example, if the maximum annual charge was 12 rubles and the maximum
allotment 4 dessiatines, the apportionment of the burden was as follows: the first dessiatine was assessed at 6 rubles; the second at 3 rubles; the third and fourth at 1.50 rubles each.

Michael Florinsky "Russia. History and interpretation"

Could you please intepret in your own words the bolded-I can't make sense- the max charges were imposed on large plots of land, right? The how could the plots have declined if thet were large. Thanks.