estimateNightActiveCombinedEnemy = (node = KC3SortieManager.currentNode()) => {
        if(!node || !node.yasenFlag || !node.enemyCombined) return;
        if(node.predictedFleetsDay && node.maxHPs && Array.isArray(node.maxHPs.enemyEscort)) {
            // only escort fleet left if all the ships sunk in main
            if(Array.isArray(node.predictedFleetsDay.enemyMain)
                && node.predictedFleetsDay.enemyMain.every(e => !!e.sunk)) return 2;
            const score = node.maxHPs.enemyEscort.reduce((acc, mhp, idx) => {
                const enemy = node.predictedFleetsDay.enemyEscort[idx];
                if(enemy && mhp > 0) {
                    const chp = enemy.hp, isSunk = enemy.sunk;
                    if(!isSunk) {
                        if(idx == 0) acc += 1;
                        acc += (chp / mhp) > 0.5  ? 1
                             // might be 0.5 instead for PT imp pack?
                             : (chp / mhp) > 0.25 ? 0.7
                             : 0;
                    }
                }
                return acc;
            }, 0);
            return score < 3 ? 1 : 2;
        }
        return;
    }
Get the escort fleet survival score from predicted day battle results,
estimate the activte opponent fleet of night battle.
@return 1=main fleet, 2=escort fleet, undefined if judgement conditions not met
@see predicted version of `api_active_deck[1]` in /api_req_combined_battle/ec_midnight_battle
@see https://wikiwiki.jp/kancolle/%E9%80%A3%E5%90%88%E8%89%A6%E9%9A%8A#wd314cc2
@see https://en.kancollewiki.net/w/index.php?title=Enemy_Combined_Fleet&diff=110224&oldid=110223