For the dual-wheel carrying assembly shown in the figure, $P$ is the load on each wheel, $a$ is the radius of the contact area of the wheel, $s$ is the spacing between the wheels, and $d$ is the clear distance between the wheels. Assuming that the ground is an elastic, homogeneous, and isotropic half space, the ratio of Equivalent Single Wheel Load $\text{(ESWL)}$ at depth $z = d/2$ to the $\text{ESWL}$ at depth $z = 2s$ is _________________.(*round off to one decimal place*)

(Consider the influence angle to be $45^{\circ}$ for the linear dispersion of stress with depth)