How can change the duration time of the siege's?

[steroid]

i have try a siege of Southampton , protect by a wall and 7100 population , 6 turn are needed . I havechange the population for 710. i have launbch a new game , and it's always 6 turn needed. I think it's more in relation with walls but nt with the population.

[dietre]

the farm lvl plays a role too.
higher farm lvl and the more fertile the land = more food production and more turns to hold out on a siege.

and i agree with aplaca that this is hardcoded