Why is the 多 in 每个月150个多小时 misplaced? I have a new teacher, and we've been communicating on WeChat.  I wrote this:

我大部分时间在自学。目前我每一天花5个多小时在学习，包括周末（每个月150个多小时），不过……

She says that 每个月150个多小时 is incorrect and it should be 每个月150多个小时.  Googling “100多个小时” (2+ million hits 101 hits) and “100个多小时” (16 hits) indicates this is indeed an error of some kind.
Question: Why is the 多 in 每个月150个多小时 misplaced?
I searched multiple questions on this topic: 1. Does 多 always come after the measure word？ 2. How to correctly use &quot;多&quot; to say &quot;more than&quot;? 3. Can you still use &quot;Number + MW + 多&quot; when the Number can be more than one MW larger?  I didn't find the answer, and sometimes putting the 多 after the measure word seems correct (e.g. 四块多美金 in this answer).  I don't get it.

I made a plot using Baidu search hits (e.g. “150多个小时” and “150个多小时”) comparing n多个小时 vs. n个多小时 (note the non-linear x-axis):

This is perhaps why I'm so confused about this.
I'm starting to feel like the logic here is that 多 represents an unspecified least significant digit.  So something like 三块五 becomes 三块多, whereas 三十五块 becomes 三十多块.  I'm not sure if this is correct.
Think of 多 after a measure word as &quot;adding some more to the previous number, without making it to the next number&quot;.
5个多小时 = 5 hours plus some, but not quite 6 hours = between 5 and 6 hours
Note that 多 follows MW 个. It means between 五個小時 and 六個小時
150多个小时 = 150 hours plus some, but not quite 160 hours = between 150 and 160 hours
Here note that 多 follows MW 十 in 一百五十. It means between 一百五十個小時 and 一百六十個小時.
四块多美金 = between 4 and 5 USD
四十多块美金 = between 40 and 50 USD