Vassal Breakup Question

so, when and how can a vassal break free from me?
is there a difference if they offered their vassalage during peacetime without me asking or as capitulation?

there are 3 criterias displayed, but how do they work?
50% of population or land is a no brainer, once they have more than 50% they could break free

but what about the % size of original? it always starts at 100%, no matter how much i shot him down during the previous war
what exactly does it mean?

When the vasal looses more then 50% of his lands since he became your vasal.

how come that they always seem to be able to break from me?

with 50% less land and pop than me and still with 100% size.

If he joined you voluntarly he can break free after 10 turns.
The 50% rule only applies if the civ becomes your vasal by capitulation.

ah ok.

what if i ask him for vassalage, without actually being at war?
does that count as voluntarly?

Yes, he voluntarly agrees to do so.
You aren't able to force him, unless you declare war and go for capitulation.

My few excursions into having a vassal having all led to trouble, I am resolved never to accept one again. But for completeness I would like to know :-
(1) Is it sufficient for a vassal to achieve only one of the 'freedom' criteria in order to be able to break the arrangement, or does he need two or even all three ?
(2) If a vassal is able to break the arrangement, will he necessarily do so or can he remain a vassal ? On what is the decision based ?
(3) How do the rules differ between voluntary vassalage and capitulation ?
(4) Are the freedom percentages based on the master's current land and population, or on those at the time of entering vassalage ? (Obviously the vassal's original land area will be 100% of what he owns when entering vassalage, and that area and his population are taken at that time - but both his values and the master's will change over time).

Politically correct note - in the above, masculine pronouns are to be taken as including their feminine forms. In my current game, Hatsheput has Isabella a a vassal.

my observations:

1. i think those conditions are only for capitulation, peaceful vassals can break free however they feel

2. the decision is based on what he has to gain.
if you can protect him from everybody else and he likes you he is likely to stay

4. current.

Only a couple of games into Warlords (one actually the WOTM1).

I particularly like when you are warring with a Civ, then suddenly peace breaks out when they "choose" to be a vassal of another Civ instead of taking further abuse from you. Just a new challenge to work through I guess?