Mark,
On 40meters, adding an 80 meter dipole to the 40 meter
loop won't 'mess' things up much. It'll change the radiation
pattern, make it sort of directional, kinda. No big deal.
But, on 80 meters, the 40 meter loop acts like a 1/2 wave
'short' between the two halves of the dipole. SWR goes up
close to around 500:1, the transmitter is looking at something
on the order of '300R - 2500J'. Not too good, and as for the
lower radiation angle, it really doesn't make a lot of
difference
at that point.
'Doc

PS - The 'numbers' are approximate, "close enough for 'gum-ment'
work"...