D&D 5E Distance and positioning of spells

[lkwpeter]

Hey there,

I was thinking about how to position areas of effect on a grid the right way. It seems important to set the point of origin correctly.

I can do that by:

a) measuring the max. range with a ruler.
b) or using the rules of movement analogously.
c) Furthermore the DMG pg. 251 states "Choose an intersection of squares or hexes as the point of origin of an area of effect..."


So my questions are:

1. If I use a ruler: Where do I start measuring? From the center of the caster's square? Because if I would choose several points along the sidelines, I would get multiple radii.
2. I also find measuring the point of origin with a ruler a bit complicated. Because how would you rule it, if you are not able to reach any of the intersections of that field? Would you also apply the 50% rule (DMG 252) and say "okay, the whole field counts"? Or would you only allow to set the point of origin on those intersections you can really reach?
3. What exactly is meant with "intersection"? Are these only the corners of a square or can I also position it along the sidelines?
4. Am I allowed to also set the point of origin within a square (not on the intersections)?
5. May I position cones also in the middle of the sidelines? (like here: i.stack.imgur.com/i9O46.png)

Would be glad about help!

Thanks in advance!

Peter