See the FAQ thread at the top of the Support forum for some diagrams illustrating the various font metrics and terms.
I design my fonts so that WinAscent - WinDescent + Line Gap = 2458 or 2048 x 1.2
This gives a default line-spacing of 12 points for 10 point text.
Pali Regular:
WinAscent = 1907
WinDescent = -551
Line Gap = 0
Garava
WinAscent = 1991
WinDescent = -467
Line Gap = 0
Sukhumala (Default line-spacing =13 points for 10 point text)
WinAscent = 1991
WinDescent = -670
Line Gap = 1
I don’t use Word, so it might calculate leading differently to Serif PagePlus