Help with correct location for the modem

Hi all,

I would like to get answers for the following question.

I live in a 40m2 apartment, and I recently switched to KPN from Ziggo.

The fiber termination is in the meter cabinet which is located outside my apartment in one of the corner. There is also a ethernet connection between the living room and the meter cabinet.

When I keep my modem in the meter cabinet I see that I get a decent signal ( -60dm) in the furtherest part in my apartment, and the speed is significantly low in WiFi when I measure speed close to modem Vs inside my house. ( Almost 50% slower).

I tried to use the ethernet connection to connect the modem in my living room via existing ethernet connection I am guessing the length is around 10 meters approx . But with this the speed is significantly lower .

I suspect that the speed is lower because of the ethernet connection between the modem and the black unit on the termination is not using the red cable and/ or the distance..

Is it possible for me to solve this issue related to speed if this ethernet connection of 10 meters is rewired with the red cable ? Or is there not going to be an improvement in the speed by doing this?