A makhraj is the point or region from which a letter is articulated; a sifah is a phonetic characteristic accompanying its pronunciation. Both help preserve the letter's identity.
For example, the two lips participate in pronouncing ب: this identifies its place of articulation. Other features, such as strength, softness, heaviness or lightness, concern the manner of pronunciation, although each has its own technical rules.
This distinction gives a method for correction: identify where the sound is made, then refine how it is produced.