Caputre Link - How to pass field value

When establashing a capture link from app A to app B only Variable, Fixed Value or NoValue can be passed as parameter to the B.
Why not a field value of A ?
How can I pass a field value of A to B using a capture link ?
Please don’t tell me I have to define a [VAR] in A assiggnit to it the value fo the field I want to pass.
It’s too convoluted to be true !