Having been a radio lines communications technican, I fitted a separate dedicated 3DB gain DAB+ antenna on to opposite side (mirrored) to the OEM AM/FM antenna, the reason for this is DAB+ works much better and has much better reception range with a purpose built antenna.
The biggest problem was finding a suitable mounting base to suit the awkward angled position.
I managed to find a disconditioned line (NOS) ball mounting base from Highway One
I get consistant reception way beyond the expected coverage maps.
"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"