How to weight in full-text search

Question

I want to search on a phrase, for example "search preference".
I want to return the phrase itself as most heavily weighted.
Next I would want to return "search" and/or "preference".
And, in lowest ranking, I would want "searching" or "searches" or "preferences".
I don't know what to put for weights in the IsAbout.
'ISABOUT(
"search preference" weight(.9),
"search" weight(.5),
"preference" weight(.5),
"search*" weight(.1),
"preference*" weight(.1)
)'
Is there a better way?