1) Efficiency gain/loss affects all units equally, a curious constant in a game that has evolved considerably. Suggest Elite units continue to recover 7 as under the current system but limit conscripts/militia to a max of 5. Better still would be to also factor Experience into Recovery as experienced units were typically able to get their act together faster. It would also be interesting to see medical-type units or leaders who can accelerate recovery (they can already inflict Shock...)
2) Allow additional units to hide in woods, towns etc. At present this is limited to infantry type units and I believe very small AT guns. Based on all of the historical accounts I have read this should include all AT guns. I would also make ANY unit in these terrain types hidden from air, or at least non-recon air. That transports, bombers etc can spot artillery in forests makes my head spin

3) At risk of provoking a firestorm I have felt for some time that non-artillery ground combat seems to favor attacking more than it should and that this is particularly evident when defending from historically advantageous terrain and/or if substantially entrenched. Not knowing the exact calculation it is hard to say if this is because of some excessive weight given to Experience, Efficiency etc but there have been countless instances where my entrenched and rested defending units in woods, towns etc were made short work of by attackers who did not have any kind of flanking or leadership bonus. As a rule-of-thumb I would say that when an attacker and defender are equal in terms of Experience, Efficiency, Strength and Attack/Defense values, an unentrenched defending unit with no terrain benefit should suffer only half the casualties of the attacker on average. I admit that it is possible I am suffering from observation bias and so perhaps the better thing would be to just share the combat calculations and see how what the community thinks.
Steve