Hello,
You are correct, while doing budget registry entries we dont have the ability to select the posting layer.
When you post a Budger registry entry, the budget is recorded in all the layers as seen below
Current
=========

Tax
======

Operations
==========

All accounts against which actual transaction and budget registry entries are made will appear in the Actual Vs Budget report
As seen above i made a Entry in "operations layer" using asset and liablity account and it appears in the Actual Vs Budget report.
Please let us know if you have any further questions,
Thanks, Kaushik
This post is my own opinion and does not necessarily reflect the opinion or view of my company or Microsoft.
P.S:- Please mark the answer as verified if it has helped you to understand the system behaviour.