Shield 'spreading'

Regarding shield damage 'spreading' (the 'overlapping shield gets 15% / 30% effect)-
Was the number (15% static, 30% mobile) supposed to be based on the shield type being 'passed' damage, rather than the shield being impacted?

I noticed that the current implementation uses the type of the shield being impacted to determine the amount of splash (15% or 30%, usually) to overlapping bubbles.

From what I read of the original topics, stacked shields being used defensively, particularly mobile ones (since they could be packed en-masse between buildings) was considered a problem. Enough to increase the 'spread' from 15% to 30% when it came to mobile shields.
(Actually, in those ancient topics, the figures being mentioned were 10% and 50%, but I can see that the current implementation is actually 15% and 30%)

I just wanted to raise this, just in case things were not working as intended, because it sounds as if the intent was to have mobile shields huddling under a static take 30% when the 'big' shield is getting hit, not 15% like they currently do.
(I also understand that the code was 'cleaned up' after it had been causing performance issues, and wondered whether this might have changed at that time)

If it's not a mistake and working as intended, then sorry for wasting your time! I just wanted to try to help!