Add more sizes to "Map icons size"

Is it possible to add additional levels of Map icons sizes?

Jumps should be 5%, or at least 10%. Will this have an impact on performance? Is 25% set on purpose to somehow lower the performance impact?

I found 100% are too big and 75% are too small. It sounds funny, but it is true. I can`t see a small geocaching icons (rectangles) on 75% when the map is full of other icons (which are a part of an image (raster) map).