its possible they deliberately increased treble at expense of bass for more range (or because of complaints audio sounded "muddy"), as on my 1990s Coomber schools receiver (100% analogue) I had to turn down treble or else I get hiss/noise from QRM (likely from VDSL/SOGEA line in here)

Some European Communications Ministries (including Ofcom UK and likely RDI NL as well) are allowing full 9 kHz audio bandwidth on AM (increased from 6,3 kHz) once more as compared to 1980s there are way fewer stations on MF (a lot of Northern European commercial stations and even PSBs have stopped using this band - its still used in Southern Europe which is why Caroline can't go to 25 kW or they would interfere with RTVE Spain (MF radio was valuable there during the major power cut)