Protection efficiency (in General)

Hi!.. If there are some who are better then me, on understanding the Prot spell, please help here:
These are the GA returns I get from 3 different familiars, all big, and all against my 39k GA.
(Damage returned are maxed, Becoming has the biggest ToJ, so I doubt the endurance on ToJs matters)

Becoming: Protection: 0
Rex's familiar fractured HypnoToad [2333]
HypnoToad's Guardian Angel smote Rex's familiar (1399)
Rex's familiar beat HypnoToad [2409]
HypnoToad's Guardian Angel smote Rex's familiar (1445)
GA ratio: 60%

Zubbus: Protection: 4
Nordeshew's familiar bruised HypnoToad [942]
HypnoToad's Guardian Angel smote Nordeshew's familiar (163)
Nordeshew's familiar tapped HypnoToad [1233]
HypnoToad's Guardian Angel smote Nordeshew's familiar (213)
GA ratio: 17,3%

Feuergeist: Protection: 13
Shield Guardian's familiar bruised HypnoToad [1971]
HypnoToad's Guardian Angel smote Shield Guardian's familiar (309)
Shield Guardian's familiar tapped HypnoToad [2210]
HypnoToad's Guardian Angel smote Shield Guardian's familiar (346)
GA ratio: 15.7%

What's interesting, is that the GA reduction between 0 to 4 in prot is HUGE (60 to 17,3), while GA reduction between 4 and 13 is quite moderate (17,3 to 15,7).

It appears clearly to me, but does this mean that Prot is following some sort of heavily curved curve?
(In that case, GA will be a pretty useless spell, unless you also have some amount of DM, to counter base protections. )
Is protection somehow making my GA to not max out, which means that I have to pump a lot more into it?
I'm happy for creative responses :)

Additional information:
This is, what my familiar puts out in damage vs. prot/not prot:

Mechanic Squirrel: (8 in prot, 0 in AC)
Hypnotized Minion's familiar crushed *whirr* [6474]
Hypnotized Minion's familiar crushed *whirr* [4427]
Hypnotized Minion's familiar crushed *whirr* [6936]
Hypnotized Minion's familiar pulverized *whirr* [6003]
Hypnotized Minion's familiar pulverized *whirr* [6891]
Average damage: 6150

Becoming: (0 in prot, 9 in AC)
Hypnotized Minion's familiar beat Rex [7634]
Hypnotized Minion's familiar pounded Rex [5152]
Hypnotized Minion's familiar beat Rex [7352]
Hypnotized Minion's familiar pulverized Rex [6598]
Hypnotized Minion's familiar fractured Rex [5638]
Average damage: 6655

My conclusions:

1).
Protection seems to punish GA very much (why, I can't figure out). Comparing the impact the 8 prot has on: GA returns/normal physical damage, gives clear differences.

2).
To successfully run a GA nowadays, you need:
. Huge GA (to counter DM)
. Huge HP (to get effect from GA)
. Huge DM (to fizzle protection)
*quite a change from CB1, where you only needed Huge HP, and a decent GA

One question:
In Becoming's AC, what part of that AC is base and what part is +.

If it is all just base AC, then I think we need to see what happens if you attack someone with + of the same level as a protection.

Perhaps they equal out.

well.. becomings AC seems to be 3+6.. but it is just a reference.. (Should have been at 0, for best results).

Since I attacked with physical, and since the GA return is physical, I doubt that "bases and +es" matters.
I think though, that 1 point of prot gives better defense, then 1 point in AC.

The main thing I want to know, is why my GA is so heavily punished by a simple base Protection, comparing to how much my normal,physical attacks are.

additional info, part two:
I have not bothered to copy+paste data, can do it, if people are interested, but a base prot does huge drawbacks to GA returns against all physical damage, and to CoBF returns..
There is no significant reduce to GA returns vs. magic though.