BJ answered most of the questions with the flashlight explanation. Great comparison or at least I think so.
wavelength spacing
1005/freq then multiply by .15
I will guess you are working on a 10 meter NVIS antenna so lets center it up on the 28.400 mhz freq
1005/28.4= 35.38 for a wavelength in feet.
35.38X.15=5.3 feet So your reflector will be placed 5.3 feet under your driven dipole, Just like BJ said, it is a yagi antenna or some call it a beam with the reflector place under the driven element.
They work pretty good for daytime rag chew NVIS on the lower bands, say 40 meters and lower in freq.
For ten meters you may want to look at a lazy H, or a 3.2 dipole for a wire with some gain.
If you have an antenna coupler (tuner) and some ladder line laying around a lazy H would be a bi directional antenna made from wires with some decent gain, around 3dbd claimed from some EZNEC models I reviewed. Heck it is even been said it works decent on 6 meters also.
Google will be your friend here for looking up a lazy H antenna.
3/2 dipole is 702/freq
702/28.4=24.7 feet per side or about 50 feet total.
3/4 wave length long for each leg. It will give you a good impedance match at the feed point. Inverted V should give you around a 50 ohm match.
I would cut each leg about 26 1/2 feet long then start trimming it to resonance, it will give you a small amount of gain over a dipole, but it will not be a figure 8 pattern it will have major lobes at 45 degrees off the end of the legs and a small minor lobe at the feed point, so if you install the antenna at the right angle you can work DX into EU, S Africa, Japan and South Pacific, all off of a wire. Of course providing that propagation is there, Mother Nature does play a big roll in that.
Coax should be run straight down from the feed point, in theory the coax is shielded and thus it should not effect the antenna radiation pattern, but everything I have researched, yes ARRL handbooks, antenna handbooks amongst others says to run the feed line directly down from the feed point.
I am no expert, I have built plenty of antennas that radiated less than the Heath kit dummy load does. But I had fun building them and trying them and heck that is all that really matters.
If you start getting serious about building antennas an antenna analyzer is a must. It will be one of the most used piece of test equipment in your shack.
Who knows before long you may be building some forced current phased arrays
I think I touched on all the questions, and hopefully created some more.
