Setting the vertical alignment to “Bottom” makes no difference, because I checked the option “Balance columns”.
Setting my measurement system to picas and increasing the height as you said did the trick. Thank you very much, David. Now I can quickly change the height of the text frame.

Hi David.
Sorry I didn’t make myself clear in my previous post.
I am trying to match the last baseline of the text frames at the bottom of the page with the last baseline of the main text frames. If you see the image, you’ll notice that the one on the right matches, but the one of the left doesn’t. Every time I resize that text frame, the last baseline has a different position, and it is quiet difficult for me to find manually the perfect spot.
The text frames have an object format with position adjusted to X & Y, and a custom baseline grid relative to the top of the text frame inset. The divider has an object style as well.
My current method to add these text frames is the following:
1. I select the last text frame from the previous spread and click the out port. There is a whole story inside these frames, and it is showing as overset, because I place it manually.
2. I create a new text frame at the bottom of the left page.
3. I apply its object style.
4. I repeat steps 2 and 3 to create another text frame at the bottom of the right page.
5. I resize the text frames with the mouse up and down until I reach the desired amount of text. The amount of text and the divider line do not necessarily match.
6. I place the dividers from my CC library.
7. I select the text frame with its divider, and I distribute the tops with Align to Key Object selected.
8. I group both objects.
9. I move the group with the cursor until the last baseline of the text frame is aligned with the last one of the main text frame.
10. I repeat steps 7 to 9 for the divider and text frame on the right page.
There must be a better method to achieve this result. It takes a lot of time to do that for every spread.