Instead of a representative month, let's look at annual statistics. This table is from the OHCHR document you linked (page 2). Even over a four year period, the numbers are about the same. In my opinion, 81.4% definitely counts as the "bulk" of something.
Civilian casualties caused by active hostilities[1]
in 2018-2021, per territory
Rebel Government No Man's Total
Territory Territory Land
2018 128 27 7 162
2019 85 18 2 105
2020 61 9 0 70
2021 36 8 0 44
Total 310 62 9 381
Percent 81.4 16.3 2.3 100.0
[1] shelling, SALW fire, and UAV strikes
There is a question of how representative these numbers are for the entire conflict, since the nature of the fighting changed after the Minsk agreements. From the same document (page 3), we see a drastic decline in deaths. Civilian deaths by year
2014 -- 2084
2015 -- 954
2016 -- 112
2017 -- 117
2018 -- 55
2019 -- 27
2020 -- 26
2021 -- 25