I forgot to add the first part: Two of my fields are:
{MERGEFIELD Client_1_Prefix}{MERGEFIELD Client_1_First \f " "}

A couple of issues here - you need to toggle the field code to add switches
so assuming yours is correct (and I haven't checked) then the correct syntax
would be {Mergefield Client_1_FirstName \b " " } Toggle back and the display
should be ?Client_1_FirstName?

Personally I prefer to use the brute force method of conditional fields to
insert data and the associated spaces or line feeds

{IF{Mergefield Client_1_FirstName} <> "" "
{Mergefield Client_1_FirstName} "}{Mergefield Client_1_LastName}

Here the construction checks for content and if there is any it moves down a
line and inserts first name and a space. The lastnamke field follows
immediately without a space. This method is easy to adapt to your
requirements and better still you can see what is happening and why. Use
CTRL+F9 to insert field boundaries {} when building the conditional fields
manually.