ffmpeg audio file cropping breaking on longer audio files

I have a bunch of audio files. I am trying to crop the first and last 10% of the files off, keeping only the middle 80%.

Essentially what I am doing:

• read file
• get duration of audio file in seconds
• use ffmpeg to crop the file from duration0.1 to duration0.9

I am using this code:

import wave
import contextlib
import subprocess
import glob

data = []
duration_L = []

for path in glob.glob('audio/*/*.wav'):
    name = str(path).split('/')[-1].split('.')[0]
    label = str(path).split('/')[-2]

    with contextlib.closing(wave.open(path,'r')) as f:
        frames = f.getnframes()
        rate = f.getframerate()
        duration = frames / float(rate)
        duration_L.append([duration, label])
        save_path = f"audio_edited/{label}/{name}.wav"
    if duration >= 3:
        command = f"ffmpeg -y -i {name_} -ss {duration*0.1} -to {duration*0.9} -c copy {save_path}"
        subprocess.call(command, shell=True)
        print('original length: ', duration)
        print("0.1 of duration:    ", duration*0.1)
        print("0.9 of duration:    ", duration*0.9)
        print(f"file should now be {(duration*0.9) - (duration*0.1)} long")
        with contextlib.closing(wave.open(save_path,'r')) as f:
            frames = f.getnframes()
            rate = f.getframerate()
            newduration = frames / float(rate)
        print('new length is:  ',newduration)
        print("\n")

It appears to work okay on smaller duration files, but it breaks on larger ones. For example, here is a sample of the print out from a bunch of files:

original length:  3.3436734693877552
0.1 of duration:     0.33436734693877557
0.9 of duration:     3.00930612244898
file should now be 2.6749387755102045 long
new length is:   2.647074829931973


original length:  4.365351473922902
0.1 of duration:     0.43653514739229027
0.9 of duration:     3.928816326530612
file should now be 3.492281179138322 long
new length is:   3.4829931972789114


original length:  8.080544217687075
0.1 of duration:     0.8080544217687076
0.9 of duration:     7.272489795918368
file should now be 6.4644353741496605 long
new length is:   6.315827664399093


original length:  12.167256235827665
0.1 of duration:     1.2167256235827666
0.9 of duration:     10.950530612244899
file should now be 9.733804988662133 long
new length is:   5.897868480725624


original length:  5.061950113378685
0.1 of duration:     0.5061950113378685
0.9 of duration:     4.555755102040816
file should now be 4.049560090702948 long
new length is:   4.08671201814059


original length:  3.3901133786848074
0.1 of duration:     0.33901133786848076
0.9 of duration:     3.051102040816327
file should now be 2.712090702947846 long
new length is:   2.693514739229025


original length:  9.195102040816327
0.1 of duration:     0.9195102040816328
0.9 of duration:     8.275591836734694
file should now be 7.356081632653062 long
new length is:   6.222947845804988

Notice that on files over ~7 seconds, the new length is not what the file length should be. Instead the file is cropped to be much shorter.

What is going on?