I don't think the toughness power needs any more refund at this point. If he is fighting evil, he goes all angel and got his powers, if he isn't, he is Joe Normal and can be hurt like anyone else. All his powers already have the +2 refund from the involuntary change, anything more would be, like Tsunami said, wringing some more points out of it.
This way, as long as he is in his angel state, he is protected against a lot of harm, even if it comes from a mundane human source. If he would, for example, slay someone who already surrendered, he would loose all his abilities until he would be able to redeem himself in some way. This would make him pretty similar to the swords of the cross, enormous power as long as they are wielded for the right purpose, fragile, if they are betraying this purpose. And in my opinion, a being like this should probably work like this.