There are two thing we could be simulating with more crits while a unit still has armor: units taking crits because a single component is stripped of armor, but other components are still protected, or units taking crits from TACs. This only really matters in terms of how it feels. TACs can feel a bit random and capricious, but give the feeling that armor isn’t magical and perfect. I think #1 has a very TAC-esque feel to it. The feeling of a robot with half its armor blown off starting to accumulate crits is different. That is more of a feeling that the less total armor you have, the more vulnerable you become. I don’t think any of the sub rations really captures that feeling that you get more vulnerable to crits the less armor you have.
I have some thoughts about how to accomplish that, but it would involve changing the AS card format a little, so it is probably a non-starter. In case someone has a way to do the same thing without card changes, here is what I am thinking. Instead of two rows of pips, one for armor and one for structure, make three rows of pips (maybe four.) armor stays on the top row and structure is split between the two lower rows. All the rows stay left-aligned like they are now. When marking off damage you start with the rightmost column and when you have filled up a column, you move to the next one to the left. Here is what this does. With armor on one line and structure on two or three, most mechs will be able to loose 50-60% of their armor in a normal fashion. Once you reach a column which includes structure bubbles, you would have to mark them off to complete the column. Hey, you just took structure damage, so the rules already say you need to roll for a crit. Easy peasy...except for the whole invalidating all existing AS cards thing!
If you can change the way in which we mark off armor and structure, you can potentially keep the idea, and the rules text, of damage to structure requiring a crit roll. You just need a reason to mark off structure before all the armor bubbles are gone. Going 2D with the armor and structure pip layout is one way to deal with it. I’m not sure if we could accomplish the same thing without changing the AS cards or not, but I think that is a good ‘feel’ to aim for: the more damaged you are, the more likely you are to take crits, even if you still have some armor.