[Tex/LaTex] Scale Standalone tikzpicture but retain text font size

Question

I have a standalone standalone_tikzpicture.tex file,

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,shapes,arrows,positioning,calc}
\begin{document}
\begin{tikzpicture}[
sum/.style= {draw, circle},
input/.style = {coordinate},
output/.style= {coordinate},
>=Stealth,
]
\node [input, name=input1] (input1) {};
\node [sum, right of=input1, name=sum1] (sum1) {$ + $};
\node [output, right of=sum1, name=output1] (output1) {};
\draw [->] node [left] {$\textbf{A}$} (input1) -- (sum1);
\draw [->] (sum1) -- (output1) node [right] {B};
\end{tikzpicture}
\end{document}

which I want to display in another file main.tex with different scale. My main.tex file is:

\documentclass{article}
\usepackage{tikz}
\usepackage{standalone}
\usetikzlibrary{arrows.meta,shapes,arrows,positioning,calc}
\begin{document}
\foreach \i in {0.5,1,...,4}{
\begin{figure}\label{fig:\i}
    \tikzset{every picture/.style={scale=\i,every picture/.style={}}}
    \centering
    \includestandalone{standalone_tikzpicture}
    \caption{Figure size \i.}
\end{figure}
}
\end{document}

Problem is, the standalone picture isn't scaled in the output of main.tex. Figure with same size is obtained.
The only way I could scale is by replacing line

\includestandalone{standalone_tikzpicture}

with

\includestandalone[scale = \i]{standalone_tikzpicture}

but this scales texts as well which is definitely not desired.
I have read Best way to include a standalone tikz file and scale it without scaling the nodes, solutions in it is not working for me. Is there a way to keep font size same and scale only picture?

Edit1 (Missed to add requirement):

\foreach is used here only to simulate multiple instances of same picture. Requirement is to use the same picture in different places. Hence standalone_file is required.

Answer 1

The following scaled inner sep to make the circle bigger, and specified the separation distance directly. I'm not sure what separation distance left of uses, but it isn't either inner sep or outer sep.

I made no attempt to use standalone. That is a separate problem.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\begin{document}
\foreach \i in {0.5,1,...,4}{%
\begin{figure}
    \centering
    \begin{tikzpicture}[
      every node/.style={inner sep={\i*.333em}},
      sum/.style= {draw, circle},
      >=Stealth,
      ]
      \node [sum] (sum1) {$ + $};
      \node [right={\i*1em}] (output1) at (sum1.east) {B};
      \node [left={\i*1em}] (input1) at (sum1.west) {$\textbf{A}$};
      \draw [->] (input1) -- (sum1);
      \draw [->] (sum1) -- (output1);
    \end{tikzpicture}
    \caption{Inner sep scale = \i, separation distance = \i em.}
\end{figure}
}
\end{document}