I mulled over the existing concept, how population and food is handled in Humankind and the Endless Games.
Especially troop management seems to be outsourced and not be part of your civilisation. This is quiet okay with Endless Space 1 & 2, where you build spaceships, but in Endless Legend and Humankind it feels odd to just build new troops for some industry points. I tried to think a bit further than the feedback I gave in openDev forum and here are my suggestions about food and population:

First of all let´s assume only a third of your total population does the work in your civilisation. The other are either kids or old people. I don´t know how much population you accounted for 1 worker (the meeple you assign to FIDSI) but let´s say it is 1000. So a small village with 3000 population will get 1 worker (3000/(3*1000)=1).
You will need 3 food/turn to feed 1 Worker/troop his kids and parents. Based on the Developments (storage, efficiency) the amount of food produced by one worker will raise. Maybe at game start the produced food is 5 regarding your fields and abilities than you might be given the option to give out more food for growth or store it for hardships. Hunting animals and raiding other settlements for food could be mandatory to avoid starvation caused by bad harvest, mismanagement or a hard winter.

Except for Scout units, a troop unit is a battalion of fighters or a comparision to strength and affords one worker to build (I don´t expect 1000 catapults in one unit BUT a catapult/tank/ship can´t be operated by a single person). If you abandon such a unit to build an outpost or for other reasons you get one worker back/it goes to that outpost. In addition you will need industry points and gold to build a unit to represent equipment and salaries.
The way it is at present you just have to pay some gold/industry to cast outposts and troops out of thin air, not properly representing the population behind it. Theoretically you can spam your land with troops without any significant impact on your economy. At least they need to be fed and while they are an army they can neither work or grow crops.

A sample scenario (Babylon, based on openDev)
We start our game with a scout unit (consists of a handful people and should have not much equipment BUT are to few to erect an outpost). We send the scouts to gather intel on our surroundings and build a farmers quarter to raise food production. Winter is coming soon, and though it might not be snowing in this region, less growth of the crops should be expected.
The scouts found a copper vein and I aim to research its usage. It might turn out to be not the wisest idea, to raise population before the winter, but I want this metal badly. Rumors spread, there might be another civilisation nearby and I could use any advantage possible, if things get ugly.
Our additional food attracts settlers as expected and we are able to build a pioneer unit for the second worker. Food consumption climbs to 6/turn, more than we produce. Now we have to be fast, build that outpost freeing our worker and get the basic production for the outpost. Now we are even again but winter will definetly put us in difficulties. Time to research fishing and sent the scouts to hunt some deer or build a hunting lodge. On their search for prey, the scouts found another settlement but not a single animal. Options are few, but we could manage to form a troop to raze the undefended village, deserting our own fields and show our neighbour some hostility or try to turn in some of our newly achieved copper. How far would YOU push humankind?

Another thought about sieges:
As mentioned above, military should be fueled by workers. When your city is under siege production is halted anyway. Why not use some "Call to Arms" where you can move your population to the reinforcement stack to man the walls? That would be peasants. I understand the three units now in the city more as a standing army, that should be slightly stronger and maybe called militia.
Why not expand the old FIDSI by one letter and rename it to let´s say ... SIMPLE (Science, Influence, Military, Production, Logistic and Energy)? Where Logistic replaces the old Dust/Money with a more wholesome term of workers who work in trade and the gathering and distribution of goods and the growth of wealth. Energy stands for food and energy in more modern environments (Endless Space 3 *wink*). Yeah, why not make it SIMPLE?