Why is the screenshot image not displaying? I am logged in. Trying again here.
This is how field sliding has worked since at least FileMaker 2.5 (the oldest version I ever used).
"Sliding up" both slides the field up and reduces its size to the minimum size needed to display the data.
"resize enclosing part" removes the "empty space" that such sliding leaves behind.
This behavior then is not the same on the PC and Mac. Resizing without the checkbox checked for "resize enclosing part" should NOT shrink the field boundaries. That's my opinion. The element should just move up without shrinking in size unless specified to do so.
Regardless, if I change the font or set the "Sliding up" on the PC, it works as I expect it to on both PC and Mac. Adjusting the layout on the Mac, gives the results as per the above noted issue where the field is resizing. It is possible that this could just be caused by the line spacing variation between Mac and PC fonts. But changing the line spacing to points did not make a difference.