I think that for the most part you have the DT/DR values in a good spot and that they all seem to be in the proper tiers to me.
I do have one suggestion though and it doesn't retain to the Power Armour's DT/DR, but instead its for their bottle cap value. I would suggest that you make their price in game much higher and make it cost a lot more to get them repaired. Their are many ways you can go on about doing this from just raising all their values all together, to pricing the different variants of the Power Armour.
If I was going to go about this I would first come up with a base value for the items in question, this time being Power Armour, and work off of that base with the rest of the items. So for my base in this I would use the T-45d Power Armour as my base, being because it is the most common of the power amours, there for will have a less over all value, and setting its rice to around 800 Caps. Sense the T-45d Power Armour is in tier one, I would make its variants around the same price. There are a couple of "Special" Power amours in the tier one and I would maybe raise their price a 100 Caps more, on top of the base value, just because their Special. As for the other tiers I would raise their prices any were from 100-700 Caps, for the base price of the T-45s Power Armour. So maybe a Hellfire Armour would go for around 2,300 caps (Fully Repaired). The reason behind this is because the higher in tier you go the more rare the Amour gets.
Thats just how/why I would raise the prices of the Power Armour and sorry for the long reasoning behind it all, I found this topic to be rather interesting. Either way Power Armour is Power Amour and I know for a fact, It will always look cool, and it will always protect you.