Here's something similar I got stuck on a while ago that I figured out, similar in OP's case where you have to detect how far/close a helper is to you to execute something, in this case its detecting how far a static helper (X and Y coordinates) is from the parent and another helper projectile the parent shoots at it to activate it into a different state, example: (sorry for the sloppy coding, it might not be the best)
Helper(1003) = Static Helper
Helper(12100) = Helper Projectile (moves across screen on x axis)
Static helper state to change state when hit by helper projectile: (Notice how I use TURN, this is really important and makes it alot easier, and then having facing in the triggers)
[State 1011]
type = Turn
trigger1 = rootdist X < 0
[State 1011]
type = Changestate
triggerall = root,facing = -1 && Helper(1003),facing = 1 || root,facing = 1 && Helper(1003),facing = -1
triggerall = root,pos y < Helper(1003),Pos y + 120
triggerall = root,pos y + 30 > Helper(1003),Pos y
triggerall = abs(Helper(1003),Rootdist y)-55 < abs(Helper(12100),Rootdist y)
triggerall = root,NumHelper(1003)
triggerall = root,NumHelper(12100)
trigger1 = abs(Helper(1003),Rootdist X)-50 < abs(Helper(12100),Rootdist X) && abs(Helper(1003),Rootdist X)+ 40 > abs(Helper(12100),Rootdist X)
value = 1006
and then this is the helper projectile code to detect the distance between it and above, and when to dissapear into a remove state, to act as if it hit the helper:
[State 4902, 1]
type = changestate
triggerall = root,facing = 1 && Helper(1003),facing = -1 || root,facing = -1 && Helper(1003),facing = 1
triggerall = root,pos y < Helper(1003),Pos y + 120
triggerall = root,pos y + 30 > Helper(1003),Pos y
triggerall = abs(Helper(1003),Rootdist y)-55 < abs(Helper(12100),Rootdist y)
triggerall = root,NumHelper(1003)
triggerall = root,NumHelper(12100)
trigger1 = abs(Helper(1003),Rootdist X)-50< abs(Helper(12100),Rootdist X)
trigger2 = time > 100
value = 13001
Like the guy above me said, my problem initially was that the actual sprite is a circular shape so i had to account for how far out the projectile helper can hit and activate it, tricky part was getting both x and y axis but it worked. using Turn and facing is really one of the keys to get this right.