Sorry your approach to communitarian and sectarian religions is too simple. The approach towards whether you ought to convert (save souls) or not (maybe you want to dominate or exterminate) is not correlated to open-mindedness.
Kharijite or Angra Mainuyi have an ancestral mentality: they are the archetypes of a sectarian religion. I could quote Teotl of course, who want to sacrifice rather than convert...
Audianism or Docetism are proselyte religions: but they are the archetypes of a non-communitarian ones.
I could continue, but I would like to invite you to have a look at the Matrix if you are interested in LI's religious features. There you will understand what is the factor that makes the Alexandros-Ammonite community communitarian, i.e. not so open-minded. It is their archaic ascendant:

Edit: I'll post an entry in Spirituality Enhancement thread on this feature to provide visibility on what are the factors. I wish I could indicate them in-game, so that an Alexandros-Amonite ruler would indicate that it is because of the Archaic ascendant. But I don't see an elegant coding way to do so.
Kharijite or Angra Mainuyi have an ancestral mentality: they are the archetypes of a sectarian religion. I could quote Teotl of course, who want to sacrifice rather than convert...
Audianism or Docetism are proselyte religions: but they are the archetypes of a non-communitarian ones.
I could continue, but I would like to invite you to have a look at the Matrix if you are interested in LI's religious features. There you will understand what is the factor that makes the Alexandros-Ammonite community communitarian, i.e. not so open-minded. It is their archaic ascendant:
- In a SELIN-mechanics perspective, Archaic civilization gives 1 point of sectarianism. This represents the fact that religions several millennia old tend to have built pretty strong spiritual boundaries to just survive. See real-life Yazidis as an example of an Archaic religion being communitarian.
- In a lore perspective, you see, this faith is not just a cult of Alexandros. It is a cult of Alexandros merged with the cult of Amon in a heavily Egyptianized version. This indeed results in this community to be considered as bordering unacceptable heresy by many who love Alexandros or Amon, while they prefer keeping to themselves as in their view every one else is wrong about both Alexandros and Amon, something close to their heart. To go further, other Greeks do not tolerate the twist on Alexandros done by Alexandros-Ammonite, and another Greek will be displeased by an Alexandros-Ammonite liege's insistence on the Egyptian nature of Megalos Alexandros. Still, they are not Sectarian, so everything remains within reasons.
Edit: I'll post an entry in Spirituality Enhancement thread on this feature to provide visibility on what are the factors. I wish I could indicate them in-game, so that an Alexandros-Amonite ruler would indicate that it is because of the Archaic ascendant. But I don't see an elegant coding way to do so.