We did some tests in our FC.

A Peisteskin map in a party of 4 people gace each one 1962g and 5 Myths, random mats and a chinchilla hide
That same map type with 8 people gave the same reward, 1962g and Myths to everyone,the same amount of random materials and also a chinchilla hide.
The last peisteskin map we used wich (lucky us) was in the exact same spot than the first one and summoned the same monster gave us 5280g and 15 myths to everyone.

Conclusion: Bring as many ppl as you can since it just generates more money and Myths. Same maps in same location with the same monsters can give vastly different rewards.