Dipole Antenna parallel laying aside in PEC Ground

Hi All

I use HFSS to simulate Dipole the Antenna parallel laying aside on PEC
Ground

I have two questions to want to ask each

1. I Dipole Antenna parallel laying aside in PEC Ground,
When depended on PEC very recently the antenna to be able by
PEC to short-circuit therefore the S11 performance was not very good.

But the far field gain unexpectedly has 8 to arrive 9dB to ask
what reason this is?

The antenna match not good radiation efficiency is not relative is not
good?

2.What type Dipole does the Antenna parallel laying aside with lay aside
in infinity PEC Ground can have in limited size PEC Ground the
difference?