3a is -58, that’s a fair reception. I have sensors with worse RSSI which work without any problem.
I’m using a +2dBi 868MHz Antenna on my self developed SPI board.
(CC1101 SPI Adapter mit u.FL Antennenbuchse – allgeek techblog)
Not sure if the second radio in your installation interferes… could you maybe dactivate or remove the second one?
Many people had success by using a 8,6cm wire antenna which they have in a small tube so that it does not bend.
All in all I’m not a fan of these generic curled antennas as you use them, see https://www.youtube.com/watch?v=ZpKoLvqOWyc