Without stacked unit concept, how damaged units didn't got this much attention. The behaviour is same with and without stacked units. The current mechanism avoided the scroll for healthy units and placed damaged unit right in front where the same type full health units.
If players wish to use, heavy, artillery and rogue units, those specific category tabs much useful with stacked units whereas "all units or first tab" if no damages units, it looks very easy from there. But, if having damaged units, mixing of heavy/artillery/rogues are expanded respectively with each of their damaged units next to it's full health units. It's affecting the stack unit real worth.
My humble suggestion is, bring one extra tab which display only full health units similar to "all units tab". Do not want to disturb current all units tab since the approach is okay without stacked units logic (may be for me). As per my suggestion, the new tab shows stacked full health units only when stacked units setting enabled. If not, it can show only full health units without stacking. If players picked them and units got damaged means, it will be visible on their respective category tab or in current all units tab. So no problem for any one. No hiding and no trouble in healing which can be maintained as usual.
Settings to players with my suggestion with or without stacked units logic,
All units tab - active or inactive
All full health units tab - active or inactive
For sure, more lag will be encountered when both tabs available, hence given settings to control it.
Problem solved, no hiccups in this!!