I checked the example Rembrandt theme and the marcmoniz.com Both of them resize the image a bit, my Davinci theme does it too, which I didn't realise. Like I said before, the images are made responsive by the themes so they will fit OK on all screens (mobiles, importantly)
My logo was resized too ... but only a little bit. I didn't even notice it till today when I checked all this.
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The marcmoniz.com logo is displayed as 220 × 40 px ... but according to the Chrome Inspect Console, the original/real size is 440x80. The theme has resized it by half. But it is still bigger than the original 177 x 44 logo. I think the theme resizes the logo up and down between 440x80 and 220x40 depending on what screen it's being displayed on. i.e from widescreen desktop monitors down to 4 inch mobile screens.
So try what Yarros did ... make your logo TWICE the size you want it and see if when it gets resized, it's the size you actually want.
EDIT: I just installed Rembrandt and tried it. It works. I uploaded a 440x80 logo and it displays as 220x40 ... the same as the marcmoniz.com site.
Case closed