I like that our units heal up while within friendly territory, but it feels like units should be better supported by specific tiles:

- Ships could heal faster while in harbours than when they're sitting in shallows

- Land units could heal faster in garrisons as well, either normally or with the help of a mid-game infrastructure (military hospital) or a legacy trait

- Finally, armies could have a reduced upkeep cost while stationed in garrisons; this would allow our empires to support more units when they're "designated defenders", placed where they can be more efficiently supplied.

well, in that case I would lower the health recovering value from 20 to 10 and I would make it dependent (alongside the upkeep cost) to the % of funds reserved to military and I would make it look like in a similar way:

150% ---> +50% recovery value/upkeepcost/moralegaining

125% ---> +25% recovery value/upkeepcost/moralegaining 

100% ---> (nothing changes)

75% ---> -25% recovery value/upkeepcost and units get a -1 CS penalty

50% ---> -50% recovery value/upkeepcost and units get a -2 CS penalty 

(I would make possible to make this value affect all your armies but also manage the singular funds% of a specific army; ex: I may have a 75% on all armies, which will suffer a -25%, but a 150% on a singular army, which will have a +50% without being affected by the -25%)

I added the "morale" to actually give more importance to this "military costs administration" and to make use of a previous idea of mine [Here's the link for a better understanding]