[D&D 5e] Why does the cone pointer have a rounded end?

Just wondering why the 5e ruleset uses rounded cones, when RAW cones should have flat ends. This causes a discrepancy when determining which grid squares are affected by a spell with a cone aoe, where the corners of the cone are affected by the spell, but are not within the cone drawn by FG.

Is there any way to change the cone pointer to use flat ends?

Quote:

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Cone (PHB p.204)
A cone extends in a direction you choose from its point of origin. A cone’s width at a given point along its length is equal to that point’s distance from the point of origin. A cone’s area of effect specifies its maximum length.

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There is no way to change the cone.
Different systems interpret the cone differently and FG needed to choose one.
It doesnt really make a big difference - because you apply the same rules to the monsters attacks.