666 Antena 1, Castanheira do Ribatejo 2×10 kW, is plagued with the same situation [see Madeira below] of power reduction.   When the old 135 kW Brown Boveri Co. txs were replaced with solid state units, the RDP chose one tx from a USA brand and one from the Canadian NAUTEL; one thereof was kept as stand by tx.  A few years ago, one of those 2 was taken away to replace a rx at some other site.  In the meantime, the only left 10 kW tx at Cast.ª do Ribatejo got a
problem, and the engineers were instructed to put it to work regardless the output: the repair doesn’t allow the tx to deliver the max. power, it’s now with just 3-4 kW, and the modulation is also low. 
The good thing is the size of the tower, but it can hardly compensate for the power & modul. loss… but the RTP administr. says MW is not a field to invest in. 
With a car radio, reception in Lisboa may be clean on 666, but a stronger audio comes from either 630 Montemor-o-Velho or 720 Elvas.
Carlos Gonçalves (2021-04-17)

1530 PEF-Posto Emissor do Funchal, Poiso (Chão dos Balcões), is another example of weak audio, at least at times, and I got the confirmation from them a few years back, explaining the changes at the new tx site wasn’t simply in terms of reduced power to 3 kW (nom. 10 kW) but also a bit of modulation level reduction so as to save components.  The Poiso site replaced the old site at Encruzilhadas, St.º António which became surrounded by houses.
Carlos Gonçalves (2021-04-17)