Subtitles and encoding mode

[dblender]

Hi everyone! I'm new to this forum.

My question is about subtitles and encoding mode.
Until not recently, I have used the default option- 'constant rate factor - single pass) under configure, when I hard coded the subtitles.
I got pretty good results, but with larger files the size was notably cut in more than 60% after I added the subtitles and chose this way of encoding mode.

Recently I came across  the "Average bitRate -two pass" option under 'configure.
and I just fill in the bit rate based on the bitRate of the 'total bitRate' of the original video, and in that way I get almost similar file size.

Basically what I want is that the output file' size will be at the quality and size of the original video (back when it had no subtitles)...so, is this the right way? is there any other recommended way of work to achieve this?

Additional details:
I always chose mpeg4 AVC(x264)) under 'video Output'.
-I always use 'copy' in 'audio'.
-Output format- mp4 muxer.

Thanks for reading my post!

[eumagga0x2a]

what I want is that the output file' size will be at the quality and size of the original video

Why size? If an encoder delivers specified quality at smaller size: all the better. Unless you want a better seek granularity by requesting shorter GOP lengths (which makes compression ratio worse), I can't think of a valid reason to want a particular bigger size.