I was putting together a bloodrager character and was intrigued by all the various reach-affecting options; I figured by tossing in some trips and crits it could be very interesting.
Let's say I have an eighth level half-orc primalist aberrant bloodline bloodrager. He has the abnormal reach aberrant bloodline power, which increases his reach by 5 feet while bloodraging. He also has the spells enlarge person (increases your size to Large) and long arm (increases your reach by 5 feet).
He has two weapons, a falchion and an orc skull ram (a reach weapon which bull rushes on crit).
(Then to capitalize on this, he has the Combat Reflexes and Improved Critical feats, Staggering Strike bloodline power (staggers on crit), unexpected strike (AoO when someone enters threatened range) and knockback (replace an attack with a bull rush) rage powers, and blade lash and rovagug's fury spells.)
With the falchion, it's easy – he threatens 5', 10' when raging, and then 5-15' or even 5-20' if he stacks on enlarge and long arm.
With the skull ram – I start to get confused. Normally he doesn't threaten 5' and does threaten 10'. When raging, does he only threaten at 15'? When he goes Large does the "Most reach weapons double the wielder’s natural reach" clause kick in and he threatens… Normally it would be 15-20 feet away for a Large creature with reach but with the extra reach is it 15-30? And with that final long arm, is it 20-40? Or since some of that reach isn't "size" reach is it some narrower band?
When combining reach extension, reach from size, and reach from weapons, how does it work? For attacking and for attacks of opportunity it should work the same, but if it doesn't let me know because I'm planning on utilizing AoOs.
I have read Can creatures attack anything within their natural reach? but it doesn't quite answer this for me.
Best Answer
Natural Reach has no impact on the Non-Threatened Adjacent range of a Reach Weapon
From the Long Arms spell:
Notice there is nothing in this spell regarding an increase to the non-threatened range, as specifically described in the section on Reach Weapons.
Your actual range would be 15'-20' from your size and reach weapon, with 5' from your bloodline, and 5' from your spell, for a total range of 15'-30'.
It may be worth checking the compatibility of Long Arms and Abnormal Reach with your GM. As both have the same effect of increasing your reach, I wouldn't allow them to stack, but that is a purely a DM decision.