Area of Effect - Cone

So i'm trying to understand the cone calculation, which in language if pretty straight forward, expecially if you are firing it diagonally. However, if you are firing it straigh ahead, the straight line language gets confusing because you end up with partially effected squares. How do you intend for us to resolve the attack for creatures in those squares?

For example, if I cast burning hands straight ahead of me, (15' cone), the first 5' is fully effected. At 10',  the second square, which by rule is 10' wide, cover one full square and half of each adjacent square. Are creatures in those squares given advantage? if so, it seems like it's to the caster's advantage to always cast cone spells diagonally. 

I realize that D&D Next has gone to feet to get away from the grid, but without the map in these kind of situations, I don't see how you are going to resolve attacks properly. 
So i'm trying to understand the cone calculation, which in language if pretty straight forward, expecially if you are firing it diagonally. However, if you are firing it straigh ahead, the straight line language gets confusing because you end up with partially effected squares. How do you intend for us to resolve the attack for creatures in those squares?

For example, if I cast burning hands straight ahead of me, (15' cone), the first 5' is fully effected. At 10',  the second square, which by rule is 10' wide, cover one full square and half of each adjacent square. Are creatures in those squares given advantage? if so, it seems like it's to the caster's advantage to always cast cone spells diagonally. 

I realize that D&D Next has gone to feet to get away from the grid, but without the map in these kind of situations, I don't see how you are going to resolve attacks properly. 



Here is the way that I have seen this handled in games where scale is used, but the rigidity of the grid is not - 1" on the table is 5' of distance, and everything is the shape and dimension it says that it is... you make a physical prop (like a cardstock cutout) and lay it on the table with the figures, and any that it overlaps are within the area of effect

ATTENTION:  If while reading my post you find yourself thinking "Either this guy is being sarcastic, or he is an idiot," do please assume that I am an idiot. It makes reading your replies more entertaining. If, however, you find yourself hoping that I am not being even remotely serious then you are very likely correct as I find irreverence and being ridiculous to be relaxing.

Any square that the line passes through is fully affected by the spell, even if only half of the square is actually in the cone. Giving creatures on the edge of the area advantage would significantly weaken the spell.
Howdy,

This is a better fit for Playtest Packet Discussion so I'm going to mosey it on down that way.


Thanks!

Monica