Sometimes you can just let the text block containing the merge field to be extra wide and over lap other layout objects. While it overlaps in layout mode, it won't in Browse.
Other times, especially in version 12, you have to be able to get the size down so that it fits inside a tab control or a portal row and there can be other reasons you need that adjustment as well.
Option 1: Don't use a merge field. If the reason you are using a merge field is to keep users from accessing the field, replace it with a regular field and use the Inspector's behavior settings to deny access to the field.
Optoin 2: In the example below, select the text shown in red and specify an extremely small font size. The field name will no longer be readable in layout mode, but the merge text will be much narrower. The size specified for the red text will not determine the size of the data displayed. That will be determined by the size specified for the black portion of the text.
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I used a merge field as it is part of a longer string of text and merge fields but changing the inner part of the merge field to 6pt font means I can still read it in layout mode and the size is uneffected in browse mode.
Thanks again for your wonderful help.
This is not a trick that I figured out all on my own. Another person shared their file here in the forum and when I opened it, I noticed this peculiar formatting and figured out by comparing browse and layout view modes why he had formatted his merge fields in this fashion.