How to acces all SubGroup computed items for a single computed product line item

I have two custom made calculation rules in my ruleset, one for single PLI prices and one for totals:

In "calculatePostpaidPrices" I create multiple ComputedDurationItems(custom defined class) which are stored as SubGroup on a single ComputedProductLineItem. This relationship can be observed here:

Now in second rule, "calculatePostpaidTotals" (on the left), i am trying to get all durations items for single PLI from first rule, now what is the way to do that (on the right is calculation result view which works fine):

Please do note that the SubGroup has been made same as in this cookbook recipe for duties subgroup: https://support.intershop.com/kb/index.php/Display/23V395#l100 But there is no example in this cookbook how to retrieve duties(which are subgroup) in next calculation rule.

After looking at some built-in platform calculation rules, I resorted to creating this method:

 private Map<ComputedProductLineItem, Collection<ComputedDurationItem>> mapDurationItemsToComputedPLIs(
CalculationRule<ComputedItem, ComputedItem, LineItemCtnr>.Input input) {
Map<ComputedProductLineItem, Collection<ComputedDurationItem>> durationsMap = new HashMap<>();
Collection<ComputedDurationItem> durationItems = input.getItems(durationsSubGroup);

for (ComputedDurationItem durationItem : durationItems) {
  ComputedProductLineItem parentPLI = input.getItem(this.durationsSubGroup.getParentCell(durationItem));

  if (!durationsMap.containsKey(parentPLI))
    durationsMap.put(parentPLI, new ArrayList<ComputedDurationItem>(1));

  durationsMap.get(parentPLI).add(durationItem);
}

return durationsMap;  
}

And then I use created map to get only duration items for specific PLI. Basically the case here is that you can't get "child" items for a PLI, but you can get parent item for DurationItem or any other item that is in subgroup and that is used in this method.