How can I adjust my Population Headroom regardless of Houses on the Editor?

In the recent DLC campaign of Hautevilles, we can see how the Population Headroom changes by Triggers. But I have no idea how to make it on the Editor.

The Campaign itself isn’t extracted unlike previous official campaigns that I can’t see how it was made.

I want to make this:
(1) Destroy a particular unit
(2) Capture the village around the unit killed
(3) Population Headroom becomes 75
(4) Kill another certain unit
(5) Capture the village around the unit killed
(6) Population Headroom becomes 125
and so on.

However, I couldn’t make it come true.

I used the “Modify Resource” effect and selected “Population Headroom” with the “Set” Operation. However, it doesn’t work properly.

My initial basic Population Headroom was 0, and by the trigger, it is supposed to provide 75. However, I got 100 strangely. I removed my 7 Houses there, and strangely again, my Population Headroom without any House is 84… What is this mysterious number? I have no idea what is going on with the trigger.

Is this a bug? Or not, how can I set my Population Headroom REGARDLESS of Houses?

Well, so far, at least the case I needed is done. I had to set two Modify Resource effects of “Population Headroom” and “Bonus Population Cap”.

The initial PH was 25 (the least and automatic number I guess), and I set the two effects with “Add” with the Bonus Population Cap, and “Set” with the Population Headroom. Now it worked.

However, still, if I break the order of capturing cities, then it works bad. Fortunately, the cities in my scenario are in order as for my visit that I don’t have to deal with this issue (maybe a bug) so far.

I will help you on here

otherwise I not wasting time typing