Hello,
Please remember to be cordial to other members when using the forum.
Pulos, for your issue, yes, shields are taken into consideration for splash damage. It would work like this.
If your p4 has 30k health and a 20k shield and your p1 has 50k health,
And your p4 is hit, and the damage that flashes up is "10,000" that means your p4 took 30k damage (20k shield and 10k health - only 10k shows because 10k was actual damage and 20k went to shield). The 30k will then splash to your other units. If your p1 has no shield, it will look like your p4 took 10k and your p1 took 30k, which can be confusing.

Does that help?