#!perl -w
use v5.16;
use List::MoreUtils qw(uniq);

my @snapshots;
my $capacity = 100.5;
my $ratio = .70;
my @keep_me = reverse uniq map { $capacity - int $_**2 / $ratio**2 / $capacity } 1..$ratio * $capacity;

for (1..1000) {
    push @snapshots, $_;
    if (@snapshots > $capacity) {
        @snapshots = @snapshots[@keep_me];
    }
}

say "@snapshots";