Scandinavia were using FM as their main broadcast platform way before the British isles so as you say, several offshore stations used it. There were very few FM stations in this part of the world back when RNI was on FM and there were none above 98 MHZ so RNI on 100 MHZ was a clear channel so DX reception was ideal. Allocating the top half of the band 2 FM band to Radio telephones and two way PMR and was a crazy move which held back the roll out of FM radio in the UK for many years until they could be cleared again.