Lilly had a section on delineating the pof. He gave point values to it in various signs, some signs had a positive point value and others were negative....imo this is quite silly as the pof isnt any better in one sign or an other, wherever it is posited you want to look at its dispositers, if theyre strong and aspect the lot by sign then it will be strong, period. Beyond that however his guidelines are pretty accurate, ie its stronger in "good" houses and if it has accidental dignities like being conjunct a good fixed star or in tight easy aspect to Jupiter or venus its stronger.
He also says its weaker when under the suns beams, which I dont buy. Its a part, not a planet, so just as say an ascendant wouldnt be weak under the suns beams, then neither would a part.