Software only encoding h264 VBR different target bitrate but similar encoded pattern???

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 hi all,  I have a question when using software only encoding in h264, VBR 1 pass mode:

the sample screenshot showing 3 files encoded from the same sequence, using 3 different VBR settings, Target20 Max20, Target10 Max10, Target7 Max7

from the bitrate viewer graph,  basically only the beginning part of the video (with some dynamic fast moving video content) reflects the difference in bitrate encoded,  the rest of the video (more like training/ static slide/screen demo style video) looks almost identical in bitrate encoded.

is this encoding behavior in Software only CPU VBR mode intentional by design?