Increased amount of powder in zinc phosphate cement mixture will cause:
Factors affecting solubility:

Powder-liquid ratio: Thicker mixes show less solubility.
Water content of liquid: Any change in the water content is accompanied by increased solubility.
Effect of moisture contamination: Premature contact of the incompletely set cement with water results in the dissolution and leaching of the surface. Varnish application over the exposed cement margin is beneficial.

Ref: Manappalil P: 91,92
Decreased strength
Decreased film thickness
Decreased solubility
Increased setting time