Hey there,
I am really sorry for the delay of this reply as it is a weekend for us here.
I've tried to access your site backend, it seems like you provided that main password no longer work, this is what i hitting :
Error
The password you have entered is not correct.
By the way, i did add your logo image into one of my test site, it seems it display correctly logo size in my Google Pixel phone, you can check my attached screenshot below, currently I do not have mobile phone SAMSUNG Galaxy Note 4 so I was unable to test this directly.
May i know do you have another Android phone so you can try and see is it only this specific mobile phone having this issue?
And also make sure your Gmail app is running latest version because the older Gmail app having this kind of issue before.