Oh also I just remembered, so for the smallMap image you can try just making that a solid blue swatch at the desired pixels instead of using "Other: Optional Things -> Run the Image Shrinker"
Just to make sure the white dots aren't coming in from that. If they only appear on the mini map it's likely from the tiny image there, where some white isn't being fully covered over by the HEX colors from the polys so they show as gaps.
Unless you have tiles that are unassigned and intended to show as white on the map, the smallMap doesn't actually need any white or black, since it's just painting stuff over from the polys there. For example the smallMap in UHD global looks like this...
smallMap uhd global.png
Only the arctic section at the very top was left white, since those polys weren't assigned in the game (to create the little ice sheet effect), but for everything else just needs a blue field to paint in the HEX colors on top. The white there was just me lazing out and not wanting to assign a ton of extra icy tiles, but if assigned and given a HEX they'll paint like all the other tiles and you just need the blue.
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For 4:3 at 320 px, try using this for the smallMap jpeg... If the little white dots don't display anymore then you'll know they were just coming from that tiny image instead of the actual polys.
smallMap.jpeg
I totally forgot, but the same thing happened to me as well! lol
Hope that helps!
ps. oh and for the shape of the polys in the mini map display, I believe it will just stretch to match the aspect there when painting the polys into the mini if it's different than the main map. Probably not a big deal usually if the aspect is slightly off between the two rectangles when showing a squiggly world shape, although to hold a simpler overall shape like a circle, I think both need to match or the circle might get compressed and go oblong? I think you're already ahead of that one cause 4:3 is optimal for tripleA. It only sorta works at 16:9 cause the Mini and UI tab can kinda cover the unused area. I'd have done the UHD in 4:3 but the regular world war II global that bung made at 2:1 so I split the difference, but it was kinda wonky at 16:9/16:10 which I didn't manage anyway, cause ended up cropping at the margins a bit. Go figure! I'm still learning how all this stuff works myself, even after many years trying to puzzle it out haha. Best of luck dude! Let me know if you hit any snags