How to align two separate comp's position

[S_ A]

I am a facing a problem and for years I feel shy to ask. Today I gather the courage to ask it. please dnt judge me. I am a naive.

Okay so in a project we have many comps, and all the comps are same in size (unless I trim that). Sometime I need to align things with two different comps. for example in attached file I want the flowers to come out from a specific part of big green box (mental health infographics) but when I open the flower comp I dnt have anything to take as a reference point about the green box’s position. I cant even copy guides from the green box’s position to flower comp. I mean am in a boat with a rudder.

I dnt wanna animate flowers and then make it a comp and then position it to another comp dragging X,Y. Is there any way I can match position of one comp's some certain part with another  like I do in photoshop or illustrator by keeping the reference layer beneath and reducing the opacity?

This question tormented me for years. Please help me if anyone can. I cant bear anymore.

[Airweb_AE]

You can use 2 viewers

Or you can use some expressions:

Add a Point Control and link the value to the position of your shape layer. 

Expression used in the video:

comp("Main Composition").layer("RED LINE").effect("Point Control")("Point")

[S_ A]

😮 😮 😮 WOW.

I wonder how many things still I dnt know! Thank you so much. glad I aksed, I feel intelligent now, lol