Maths time! I thought I'd work out the effect of this suggestion relative to the current position. In all the examples I've looked at 4 dice v 4 dice. Although I've compared Heavy Armour to Armour the calculations work for any better armour case.
So, first up looking at the case where there are no other POAs involved, here are the average number of hits (including rerolls where applicable) for a 4 dice each combat:
In this instance the better armoured troops are the same but those with worse armour are better. This difference equates to a level in grading, e.g. Superior Armoured troops and Average Heavily armoured both score 2 hits.
Next up is the situation where the better armoured troops have another POA in the current system:
In this instance both inflict less hits, the HA because they're only hitting on 4s and the others because their re-rolls are worse. The overall effect is dependent on grade, looking at the relative number of hits:
Superiors are better off, in the current system the Armoured troops inflict 49.5% as many hits as Superior Heavily Armoured. In the proposed system they inflict 56.7% as many.
However, Average troops are marginally worse off, with Armoured inflicting 49.5% as many hits as HA, currently but only 43.9% in the proposed system.
Poor troops really suffer. They inflict 40.5% currently but only 26.1% in the proposed system.
Finally, we have the case where the Lesser armoured troops have a +POA of their own:
In this case, which is evens in the current system, the lesser armoured troops are better off. They're losing out on the re-rolls but the better armoured troops are now hitting on 5s.
For me, there are 2 major concerns with adopting this system:
1) It would not make sense to adopt it for mounted combat only. Since that is the area that has been identified as being currently an issue, do we want to introduce a system that then impacts the foot interactions which seem generally satisfactory?
2) Although this does provide a good solution if all else is equal (with better armour having exactly the same effect as a higher grade, which is generally regarded as half a POA), the effects where other POAs are included don't seem to be sensible. Poor and Average troops would be worse off than currently if there's another POA against them and combats that are currently even become potentially very swingy.