Large Creatures, Reach Weapons, and Armor Spikes

[erok0809]

If I have a large creature (natural reach 10 feet) wielding a glaive and armor spikes, does he threaten 15-20 feet away with his glaive and 5-10 feet away with his armor spikes? Or is it only 20 feet away with the glaive?

It seems odd that something that didn't have variable reach (only able to hit 10 feet away) before now does have it, when the length of (arms+weapon) is still constant, just bigger than earlier.

For the armor spikes, how am I supposed to explain someone 10 feet away being hit with armor spikes in-universe? I can understand it for 5 feet away, where he does like a shoulder charge for a mini-bull rush kind of thing that just doesn't actually move them, but that seems odd for 10 feet away where that explanation wouldn't really work.

Can someone clear these up for me, preferably with a rules answer followed by plausible in-universe explanations for what's going on?

[Flickerdart]

Straight from the rules on reach weapons, we have this: "A typical Large character wielding a reach weapon of the appropriate size can attack a creature 15 or 20 feet away, but not adjacent creatures or creatures up to 10 feet away."

[ComaVision]

If I have a large creature (natural reach 10 feet) wielding a glaive and armor spikes, does he threaten 15-20 feet away with his glaive and 5-10 feet away with his armor spikes?

Correct.

You can hit someone 10 feet away with armor spikes by colliding your spiked arm to their vulnerable face.

[erok0809]

I guess that works as an explanation; I always thought of attacking with armor spikes as more of a tackle/body blow kind of thing, but I guess the arms have spikes on them too, and you could just swing those around, yeah. Cool.

What about the glaive suddenly being able to hit both 15 feet and 20 feet away? It doesn't seem like his arms would suddenly be more flexible where it could hit shorter than (arms+glaive) length, which is approximately 20 feet. I guess I could say he chokes up a little to hit shorter at 15 feet, but that's like the whole purpose of the Short Haft feat, which he doesn't have. I guess I could say he chokes up only a little?

[ComaVision]

What about the glaive suddenly being able to hit both 15 feet and 20 feet away? It doesn't seem like his arms would suddenly be more flexible where it could hit shorter than (arms+glaive) length, which is approximately 20 feet. I guess I could say he chokes up a little to hit shorter at 15 feet, but that's like the whole purpose of the Short Haft feat, which he doesn't have. I guess I could say he chokes up only a little?

You could explain it like that. I mean, the blade of the glaive is a lot larger for a large creature too so if the midpoint of the 3'+ blade is between the 15' and 20' squares then I could see it inflicting damage to foes in either one.

[OldTrees1]

I guess that works as an explanation; I always thought of attacking with armor spikes as more of a tackle/body blow kind of thing, but I guess the arms have spikes on them too, and you could just swing those around, yeah. Cool.

What about the glaive suddenly being able to hit both 15 feet and 20 feet away? It doesn't seem like his arms would suddenly be more flexible where it could hit shorter than (arms+glaive) length, which is approximately 20 feet. I guess I could say he chokes up a little to hit shorter at 15 feet, but that's like the whole purpose of the Short Haft feat, which he doesn't have. I guess I could say he chokes up only a little?

Fluff reasoning:
The arms are 5-10ft in reach(not length). The glaive is about 10ft in length. 5-10ft + 10ft = 15-20ft. Choking up would require bringing in the arms inside the 5ft reach mark (just like it means for medium sized creatures).