Unity ARKit image tracking

Hi, I'm building a Unity ARKit mobile app these days: there are several 3D models in prefabs showing up in 21 rooms/places of a museum, so I had to use image tracking to have one model per place.

Although most of the app works, some models don't show up.

I have a few questions/topics:

- it seems the tracking is affected by the number of reference images to be tracked

- lighting is important, so I had to use day and night reference images.

- in the Unity ARkit package, there is a "MaxImages" parameter, is it relevant and if I put 20, it would stop tracking the images in the reference database after index 20?

- are there other parameters I can tweak to help tracking? it seems I don't have much control on other parameters, if any.

Thank you for any hint!