Scale watermark to fit on different video sizes

I have a watermark.png that was made to overlay videos with 1280 width. When i use a different size video, the watermark is totally out of proportion.

So i'm looking for a single command that can scale the watermark to fit the original video size. I do not want to resize the original video.

This is the current working format i use which works fine with 1280 width videos. (watermark placed left-bottom)

-i video.mp4 -vf "movie=watermark.png [watermark]; [in][watermark] overlay=1:main_h-overlay_h-1:enable=not(between'(t,30,210)') [out]"

On a side note, since the watermark is simply a 15 letter word i could also use text in the command if this would make the solution less complicated.

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