Map Sustain

I got a question about sustaining t16 maps. I have all my voidstones allocated. My understanding of map drops is that lower tier maps do not drop due to my voidstones but instead are credited to getting a t16 map. I can get credit for 3 t13 maps for 1 t14 map and 3 t14 maps for 1 t15 map and so on until I get a t16 map. Do this mean natural higher tier maps are easier to sustain since they are dropping credit for higher tier maps? The two popular maps I've seen are cemetery and jungle valley. Is jungle valley easier to sustain because it is a naturally higher tier than cemetery?

I am fairly certain that whole credit system was removed fairly shortly after it's introduction because people complained about not getting any maps at all from stuff like delve cities. You can and will drop lower tier maps even if your entire atlas is tier 16. I don't think there are any differences between the sustain of different maps.

If you want to sustain 1-2 favorite maps, it's easier with less voidstones, because there are less maps of that tier in your atlas.

For Jungle Valley, if you're ok with it being T15, it's easiest to sustain with a single voidstone. With a single voidstone, there are 6 T15 maps, one of which is Jungle Valley. With 2 voidstones you make Jungle Valley T16, but then there are over 40 T16 maps that can drop, so you need more favorite map slots to sustain.