Surface deflection, as like as stress/strain, is a pavement response which may be considered to be dependent upon various internal and external factors. Internal factors, i.e. material specifications and characteristics, are those which are usually selected to produce different types of asphalt mixture, and base/subbase courses; while the external factors, e.g. loading frequency, aging condition, temperature, etc., are related to different traffic and/or environmental conditions to which the pavement may be exposed.

Surface deflection depends exencialy to the materiasl properties (undes some condition to aging, temperature, wet) and the thickness of the layers.

Both concepts are  correct but subgrade compaction also affect the surface defection.

In addition to the above statements, asphalt binder properties i.e. viscosity, play a significant role in the formation of surface deflection. Beside traffic loads and overlay materials properties, in situ volumetric properties can also affect surface deflection. See the following references:

I think generally a lot depends on material specification and design

Surface deflection is materials' response to traffic loading and hence it is dependent both on materials properties and loading conditions (coupled with environmental factors such as moisture, temperature, etc.). Materials include asphalt layer, base/sub-base and subgrade. And, any of the layer or all together may contribute to the overall deflection of the pavement.

One of the major reasons for the deflection is the permanent deformation (or, rutting) of the asphalt layer, unbound granular base or the subgrade. Properties of asphalt you may consider responsible for rutting are binder type and mixture characteristics such as dynamic modulus and phase angle. For unbound granular base/sub-base, you may consider resilient modulus, matric suction, fines content, etc. Subgrade properties may be the subgrade modulus and strength. These properties are very much influenced by some factors in the field during road construction. For example, moisture content and compaction for unbound granular base/sub-base and subgrade OR temperature, plant mixture characteristics, compaction, etc for hot mix asphalt.

Loading conditions that may be responsible for excessive surface deflection are axle load, tyre pressure, loading frequency, etc. Severe environmental conditions such as excessive moisture in the subgrade, base and sub-base OR high temperature in an asphalt layer may also be of great concerns for smooth performance of a flexible pavement in terms of surface deflection. 

1- The stiffness of each layer

2- Thicknesses

3- Tempreature at testing

4- Frequency of the loading process applied by the testing equipment

Slurry setting time is dependent on the environmental condition. Slow setting time usually it takes longer time to cure and break. Generally for cold weather rapid setting will be encouraged because it takes longer time to cure and break especially at  night.

I think the stiffness of all the layer contribute to the surface deflection..the stiffness of asphalt concrete layers effected by several variables like asphalt cement properties (content and grade) as well as aggregate gradation and filler type and content. also the stiffness of granular material is highly effected by the material gradation as well as the water content. 

beside the material stiffness the layer thickness plays an important role in the surface deflection..the thin layer is probably more susceptible to surface deflection.

all of the above considered internal factors we should not forget the external factors like the ambient temperature which could reach in arid area to 60 degree celsius and that mean the temperature of asphalt concrete layer in the surface will reach 70 degree celsius so the asphalt concrete ;ayer will loss approximately 70 percent of its bearing capacity due to the deterioration in its stiffness value. in the other hand there is axle loading, the excessive axle loading defiantly lead to more surface deflection in pavement surface.