I will try spamming lowest and see if it takes more then 20 after first rank up.
Unless SE ninja-changed something (I sure don't remember reading anything about that in the past 2 years' patch notes) I can 100% confirm it's like that.
Before we found out the
"20 to rank up but only if you use current rank ones" rule, it took me ages to get rank ups.
It was 20 at first, going up to 30, then 40 and even higher.
Still some people were reporting "I got rank up with 36!" or strange numbers that we couldn't understand on BG or FFXIAH.
We all believed "you just miscounted!" but in hindsight the truth was that those people did low ranks plus a couple of current ranks, and that's why the numbers were different.
I mean, feel free to spend your time doing your test, but it 100% used to be like this and I'm skeptic on SE changing anything big about it.