Primary and Secondary image targets

Hello!

I have A4 format paper sheet with the image on it but it has a white blank rectangle to be filled with a sticker in future to complete the picture like a puzzle game.

Vuforia should detect this paper only once it's completed and should not if it has not filled yet zone.

Very basic solution is to track only that quad sticker so it will work only if it is already attached to the sheet. The problem is that this piece has too few feature points and has 1-2 stars as an augmentable rating.

I decide to make an advanced solution which consists of two image trackers. One for inner quad (primary) and the second for entire sheet (secondary).

When we will move camera closer to the quad it will activate model on the entire sheet and model will not be hidden when this quad will be lost.

Model will hide only when entire sheet will be lost.

So, to show model we need to move camera close to the quad inside and once it's done the model visibility and position are related on the entire sheet which has 5 star augmentable rating and provide a good stability and quality.

My problem is that the inner quad is very hard to detect when all sheet is already detected. If i move the camera close to the inner quad before launching the app to force app detect the quad first and only after that detect entire sheet i achieve a nice results.

But, if i run my app and after that i starting to move camera close to the quad (sheet at this time already tracked) quad is ignoring. Can i somehow add some priority to the image targets or force vuforia to detect both image targets even if they are one inside other?

Also i noticed that only first recognition is so hard. If image target has been detected at least once it's very easy to detect as long as i want even if it becomes lost. Why? When inner quad has been detected i can easily move camera out from the sheet scope and return it back on a pretty big distance from the entire sheet and it's work just perfectly. Even tested on the same sheet with a blank quad and it doesn't showing model (work correctly) ,so it can actually see the inner quad from that distance but why it doesn't do this at the beginning?

Here is a video example of the problem: https://youtu.be/KbfU4oOYn14