Relationship between warp and weft spacing
Sett (s.l.) comes in 2 types:
The spacing of the warp threads, or ends, usually given in ends per inch (epi). The warp sett (or sett s.s.) is fixed once the loom is completely dressed; changing it means cutting the warp and resleying the reed.
The spacing of the weft threads, or picks, usually given in picks per inch (ppi). The weft sett is adjusted at each pick, and is also known as the beat (in meaning (3) in the glossary).
There is a tight relationship between the warp sett and the weft sett.
If you have a tighter warp sett (higher epi), the weft yarn won’t have room to move up and down around the ends and picks will be less tightly packed (a looser weft sett, i.e., a lower ppi), and the resulting fabric will show more of the warp (warp-dominant fabric).
The converse is also true: a looser warp sett will allow more room for the weft yarn to find its way around the ends and will pack tighter (a tighter weft sett, i.e., a higher ppi).
This holds if you apply roughly the force to place the pick in the shed (beat in meaning (2)). You can keep the same ppi with a looser warp sett if you beat softer. On the other hand, you can only to compensate so much for a tighter warp sett by beating harder.
And of course, the resulting cloth will be different!
The challenge of choosing sett(s) is picking a warp sett that allows you to beat comfortably yet obtain the cloth you want.