Assuming that CPDN still uses an older version of the server side scheduler, that is happy with only 2% success results, which would be this one :

void SCHEDULER_REPLY::got_good_result() {
    host.max_results_day *= 2;
    if (host.max_results_day > config.daily_result_quota) {
        host.max_results_day = config.daily_result_quota;
    }
}

void SCHEDULER_REPLY::got_bad_result() {
    host.max_results_day -= 1;
    if (host.max_results_day < 1) {
        host.max_results_day = 1;
    }
}

The 2% are a worst case scenario, example :

Host limit is 100 results/day, after "burning" 50 results it is reduced to 50/day. A singe success result is sufficient to bring the limit back to the full 100/day so the cycle can start over.

this might be changed into this one, that has a harder penalty for bad hosts :

void SCHEDULER_REPLY::got_good_result() {
    host.max_results_day += 1;
    if (host.max_results_day > config.daily_result_quota) {
        host.max_results_day = config.daily_result_quota;
    }
}

void SCHEDULER_REPLY::got_bad_result() {
    host.max_results_day /= 2;
    if (host.max_results_day < 1) {
        host.max_results_day = 1;
    }
}

In later server side BOINC versions the coding in sched_result.cpp is somewhat different but it basically still handles bad/good in the same way, e.g. :

good :

    int n = havp->max_jobs_per_day*2;
    if (n > config.daily_result_quota) {
        n = config.daily_result_quota;
    }

bad :

    n -= 1;
    if (n < 1) {
        n = 1;
    }

which could of course easily be adjusted in the same way.