Making the pope call crusades or making more factions join yours

[FactionHeir]

Well, I got a bit bored of myself calling crusades and almost never anyone joining in. Looks like if the pope calls one everyone joins.
So...how do I make the pope call crusades OR make more factions join in my crusades? Faction standing / Global reputation does not seem to play a role in that as far as I can tell.

Only reference I found was this:

<crusades>
      <required_jihad_piety int="4"/>
      <max_disband_progress float="20.0"/>
      <near_target_no_disband_distance float="4.0"/>
      <disband_progress_window float="3"/>
      <crusade_called_start_turn float="20"/>
      <jihad_called_start_turn float="20"/>
      <movement_points_modifier float="2.0"/>
   </crusades>

in the descr_campaign_db.xml
I'm not sure what the called_start_turn means, but it certainly does not mean the pope calls a crusade at that turn/year count, as I tried it with 10 instead of 20 (i.e. it will then either mean 10 years or 10 turns)

[Re Berengario I]

called_start_turn 20 means that crusades will be called by the pope just after the 20th turns of playing.

About the joining of crusades, etc it's determined by a lot of factors the most important of which are having some troops and familiar members at free disposal together with a bad relationship with the faction the crusade is called against.

[alpaca]

The pope dishes out missions if he calls for a crusade himself which is why a lot of factions join in then.

[FactionHeir]

The pope also gives out the missions if its you calling the crusade though, so not sure if thats linked to it or not.