On the band where a dipole is 1/2 wavelength long (20M for the G5RV) the maximum signal will be off the sides of the antenna
Except, that on 20M a G5RV is three half waves long. The dominant lobes of a N-S oriented G5RV are NE, SE, SW and NW.
The bottom line is that I wouldn't worry too much about the direction it is installed for 40M and especially for 80M.
Even at only 30 feet up a G5RV has quite dominant broadside radiation on 40 and noticeably so on 80. Enough that it would matter to me anyway.