FormattedHeight of a field and its contents

[David Epstein]

Is there somewhere an explanation of how a field’s textSize, borderWidth, margins, and formattedHeight interact?  

According to the dictionary entry for “formattedHeight”, a field’s formattedHeight is calculated “including top and bottom margins”, while the formattedHeight of a chunk is calculated “disregarding margins.”

That does not seem consistent with these results for a field whose textSize is 16 and whose margin is 4:

the formattedHeight of line 1 of fld 1                 19
the formattedHeight of line 1 to 2 of fld 1          38
the formattedHeight of fld 1                               15  if there’s one line of text
the formattedHeight of fld 1                               34  if there are two lines of text.

Even though there are top and bottom margins of 4, the field’s formattedHeight is smaller, rather than larger, than the formattedHeight of its contents.

A perhaps related question:  Why does a field margin of zero clip the visible text at the top and left?

Many thanks.

David Epstein