Maybe somebody can shed some light on the following matter:

Recently I have installed an 18 GHz Microwave link, consisting of NEC-
Pasolink gear and Andrews Microwave Dishes.
Because it was a first for me, I had thought over the process of lining
up the dishes. I had heard of and read about the side-lobe vs the main-
lobe.
So I figured out the my coworker on the other end of the link should move
his dish and I would tell him the reading on my voltmeter. The higher the
better and at the peak reading he would fix the dish. Then I would do the
same on my end. And then his end a second time and then my end a second
time
We would repeat this procedure for the vertical line-up as well.
I had calculated an expected attenuation which could be converted in a
voltage reading.

Assume the reading should say 3,5 V. Well I never got anything better
than 2.8 / 2.9 volt.

COnsequently I asked NEC for advice and they said that 'you should line
up you own end using the voltmeter, and not the opposite end'. With this
advice we repeated everything and reached the expected reading of 3.5
volt. The 2.8 volt was a sidelobe of the antenna-beam

What I don't understand is that when I rotate my dish (either
horizontally or vertically) I can go from sidelobe to mainlobe to
sidelobe. I don't move the dish further left or right, I only rotate it
around a vertical or horizontal axis. When I would move the dish further
left or right or up or down, than I can visualize going from lobe to
lobe. Not by rotating the dish
That is why I used the opposite end to move the beam.

Anybody can explain where I go wrong

Regards, Ad