the ground was set to "free space" and when i selected "perfect" ground

an error occured "one or more wires extended into or lying on the
ground", the problem was that in the wire coordinates z was set to 0
,when i selected a different z the problem was solved but the voltage
is still high, the antenna will be placed 90 deg. to the ground plane
so what should be z value?should it be the same length of the antenna?
the source is placed 0% from E1 (monopole). the pattern of the antenna
shows a gain of 1.5dbi ,if i have a circuit that outputs 2db for
example then the output from the antenna should be 3.5db, right? or
because dbi is referenced to isotropic source there is a conversion?
note: i can't upload the file rightnow