I need help understanding about the Pathos Heritage unique behavior

this is a better repost of a question I placed before, hopefully easier to understand.

I bought a Pathos Heritage for my home in the USA, when it arrived I opened it and put it in the rack, and let it seat for 2 days as it was delivered in a wooden box without any plastic wrapping so I assumed that after crossing across the Atlantic in a boat there was some humidity that hopefully after 2 days sitting with a small fan blowing would be gone.

Then I powered it on for a little over than 2 hours before playing music, but to my surprise at 50% volume the sound was scary low for a 80Wpc amplifier, with pretty efficient AgantGrade Duo Mezzo XD and Tannoy Kensington speakers.

Here is a REW measurement in the first few hours.

So I let it run overnight and in the morning I noticed that it was louder, which I checked with REW and it was louder.

I had to go to CA for work for 2 days so I left the amplifier playing for 2 1/2 days. When I came back I can hear the music from the driveway. My house is a good distance 50-60 yards from every other neighbor.

I checked that the volume was still at 50% and now the am is playing so loud I could not stand it. So I measured again after about 100hrs of continuous play.

I have owned and own a lot of amplifiers, I have experienced some increase in loudness and a lot of sonic improvement, but never anything like this and I don’t understand how this can happen.

The amplifier sounds very good for the money, so I am looking forward to keep the sonics improving.

Maybe you can help me to understand how this can happen or if this is a normal thing for the Heritage?

Thank you