It does work. It is easy to do. It is not so easy figuring out how to do it, but two of us have given you step-by-step instructions.
One step was neglected, though, to place a left tab near the left margin. I suspect that this was because we are unused to putting a decimal tab inside a table. You are right that with a decimal tab, unlike the other tab settings, in a table text aligns to that tab immediately, unless there is a tab setting before it.
I will be adding a
section to my chapter on
Tables about this.
See the attached file and screenshot.
Reminder: Once you have a setting you like, it is good practice to use this setting to define a paragraph Style. If you do that, you can apply the Style whenever you want it. More important is that if you change the size of your table cells, you can modify the Style and have it change throughout your document.