Here is a photo of my setup. Window is facing North. I am able to get 100l% on channel 9 and 27% on channels 2 and 4.
27% is just not quite enough to view channels 2 and 4. Signal is trying to come through. Screen is mostly black but you can see some color trying to come through.
There is a test that you can do that is very inexpensive. You can buy an RTLSDR dongle and learn to use the free spectrum analyzer software for it to see what your channels 2 and 4 look like at your location.
The dongle is only about $20 US. It plugs into a USB port on your computer. It doesn't come with the software; it will be necessary for you to assemble the software in a folder. If you have trouble assembling the software, there is a tutorial thread that will help you.
Forum member lenlab
was able to do it so that he could see what was causing interference to his reception of VHF channels 7-13. This is his thread:
This is his scan that shows noise interference on VHF 7-13:
For comparison, this is what my channels 7-13 look like; 7 and 13 are OK but 9 is marginal:
This is the SDR dongle with an antenna adapter cable:
I did a test scan for channel 3 that shows a very high noise level from electrical interference on VHF:
The signal had just enough SNR above that high noise level for good reception:
If your channels 2 and 4 don't have more than 15 dB SNR above your noise level, try to find a location for the antenna where the noise isn't as strong.