EB2 already solved the issue by using psf´s as secondary cities who can better represent those hard to reach places

plus with the new system of the top 5 units not costing upkeed in a city and up to 2-4 units in a psf not costing upkeep (wich will probably be scripted to double for eleutheroi i suspect) i believe the sistem is almost perfect atm concerning your concerns and we can have a more balanced game experience and with probably less blitzkrieging

p.s: psf = permanent stone forts

if you´re a player like me i guess you already discovered that for us we´re screwed in securing our borders in rivers setting up forts at every pass to gain time to react so we can only hope the ai isn´t that dumb as to attack without analysing the odd´s 1st