How to control flattened drop shadow ppi?

[7x8]

I'm creating some files for printing, page size 100x550mm, scale 1:10. I have one object with InDesign's drop shadow.

And after exporting (no downsampling, flattener set to 1200 ppi for meshes and gradients) flattened images resolution is 529.167 ppi. When I scale up page size to 200x1100mm, exported shadow is 264.583 ppi all of a sudden (checked with Acrobat's preflight). In both cases I'd expect it to be 1200 and I need this shadow to be effectively at least 120, 150 would be optimal. Any clues?

I really don't want to recreate these in Photoshop...

[Frans v.d. Geest]

Lets start with: why do you want to flatten in the first place?

[7x8]

I don't want to 😉 Printing house guidelines, but I suppose that's beside the point, I'm really curious what's behind variable drop shadow ppi vs flattener settings and if there is any chance of controlling them.