That seems rather counter-intuitive. Persuading Lords while at war seems rather risky, not to mention good luck catching them while out of an army. Wouldn't defecting while at war be more dangerous and heinous for the lord in question? I mean when they do that, they are actively betraying their former Kingdom and allies.
During Peace time, I mean yeah it's kind of treasonous, but could be considered just moving or "border negotiations".
To me it should work the same regardless of War/Peace. You've either got the Charm/Relationship/Power to convert someone, or you don't. Kind of invalidates Charm if it only works sometimes (and no Quests/Marriage are not worth Charm skill) when the game decides it's okay.
Honestly if you're charming enough, liked enough, rich enough - why shouldn't you be able to convert most anyone? To me the formula should be relatively simple:
(I guess you can keep the silly RNG conversation beforehand, but no one likes RNG honestly)
Conversion Score = [(Charm/50) * (Kingdom Power Ratio*25)] + Relation
*If conversion score is or more 100 they'll consider converting; if you can pay them enough
**Kingdom Power Ratio should be decided as Your Kingdom Score (Towns = 3, Castles = 1, 1000 Troops = 1) / Their Kingdom Score
Conversion Cost = [(Their Clan Score*50) / Conversion Score + 1/(Charm+1)] * 1,000,000
*Clan Score is tallied same as Kingdom Score (Towns = 3, Castles = 1, 1000 Troops = 1)
So for example you didn't invest in Charm and only have 20 Charm Skill, but you somehow buttered up the last remaining non-Ruler Clan to say +25 Relation, and your Kingdom is pretty strong at 14 Towns and 14 Castles. Where their Kingdom is on the brink with 1 Town and 1 Castle remaining. They got say 1500 Troops total, yours has 9000 Troops -
Kingdom Power Ratio is 11 (always round up/down)
You were able to convert them half due to your power and half due to your relation, a total
Conversion Score of 135
Now this last holdout Clan has 1 Castle and let's say 500 Troops, so you'll have to pay quite a bit still with a
Conversion Cost 788,000 denars. But if they had no fief at all and only 200-300 Troops,
they'd join you readily for 47,000 denars as Conversion Cost!
Case in point fiefs are expensive so maximizing your Conversion Score goes a long way!
But let's say the Kingdoms were totally equal in power...
Conversion Score is only a measly 30, so no chance at all
But let's say same scenario, only you had leveled up Charm to a somewhat high 175
Conversion Score is 108
Again let's say they have 1 Castle and 500 Troops -
you're going to have to pay 931,000 denars in Conversion Cost to turn them this time.
Finally let's say you've really power game'd and your Kingdom controls half the continent (27 Towns, 32 Castles, 18,000 Troops) and you got like 275 Charm. You're pretty much guaranteed to be able to convert clans, but how much will it cost you?
- Let's say you have a bitter rival (-100 Relation) in a smaller Kingdom (4 Towns, 4 Castles, 4000 Troops). Conversion Score is 801. They have 1 Castle and 500 Troops. You'll have to pay them 128,467 denars as Conversion Cost - and this is where the building up your power and your charm has guaranteed you total power
- Let's take a neutral rival (0 Relation) in a smaller Kingdom (4 Towns, 4 Castles, 4000 Troops). Conversion Score is 901. They too have 1 Castle and 500 Troops. You'll have to pay them 114,000 denars as Conversion Cost
- Finally say there is a 3rd Kingdom fairly large (10 Towns, 14 Castles, 10000 Troops). Rival clan somewhat dislikes yours (-30 Relation) and they own 1 Town, 2 Castles, and 1000 Troops - a sizable force. Conversion Score is 304. Conversion Cost is then 990,000 denars.
And to recap these last 3 if you basically had little to no Charm (say 20) but same large Kingdom...
1. Small bitter rival no conversion
2. Small neutral rival, Conversion Score 164, Conversion Cost is 613,000 denars
3. Large rival no conversion
Well wasn't planning to write my thesis, but there ya go. See no random incomprehensible stuff, simple obvious results even if you don't know the maths. Early on converting Clans to your Kingdom is largely impossible or going to be very expensive and thus a significant event. If you make it to the end game, leveled up your Charm, you can now sweet talk the rest of Calradia to join without any bloodshed.
And no sillyness based on War or Peace. As the immaculate Todd says: