Cutting Frame Rate in half during conversion doesn't change file size

I am converting .wtv files from Windows Media Center to .mp4 files. After doing a conversion to a 1280 maximum width, the final file is about the same size as the original .wtv file. So after reading through this site I found that I could change the frame rate of the converted video by altering the -r command in the mcebuddy configuration file. I, incorrectly apparently, figure that if I halved the frame rate and kept everything else the same, the file would be about half the size. I was surprised to find the result was only 6MB less in a 3GB original file.
The original .wtv file was 3.347GB.
First conversion with maximum width set to 1280 and -r auto set in the config file for frame rate, the file size was 3.040 GB. Details showed the file to have a resolution of 1280x720 and a frame rate of 59 fps.
The second conversion kept the width set to 1280 but I changed the -r command to -r 29.97. The resulting file size was 3.034GB with a details showing a 1280x720 resolution and a frame rate of 29 fps.
What am I missing here? Shouldn’t cutting the frame rate in half, take out half the frames and significantly reduce the file size? Any help would be appreciated. Thanks.
System: Windows 7 and MCEBuddy v. 2.3.13.

You can change the frame rate from the expert settings page:

Thanks. Apparentlly that Expert Settings page doesn’t exist in v. 2.3.13 which is the version I have been trying out. I manually changed the setting in the configuration file. As stated above, the files show the frame rate as being changed but it didn’t change the file size which is puzzling to me.