Point Blank PD Mode "X"

[Beaker (OP)]

In the Combat Assignments Overview screen, when I set a fire control to a certain Point Defense Mode, the summary in the lower right hand corner will read something like  "Point Blank PD Mode 3."  I only use final fire, but sometimes that assignment displays as "Point Blank PD Mode 3" and sometimes "Point Blank PD Mode 5."  Sometimes when I go back to confirm final fire on a ship, I will see it change from 3 to 5 (or vice versa) even though I never use any other setting.  I would say this happens about 1 in 3 times. Does anyone know why the modes seem to float around this way?

[MarcAFK]

You have me stumped, if nobody can explain it perhaps some science is in order.

[Iranon]

Point Blank means it'll only fire when something is about to be hit, it does NOT mean the vessel to be defended has to be in the same spot (recently tested).
the "Mode" is just the maximum distance to which it will engage missiles, in 10k increments.
This usually doesn't feature much, but combined with formations this allows you to reserve point defence for certain assets (e.g. dedicated sensor vessels).

[Beaker (OP)]

You have me stumped, if nobody can explain it perhaps some science is in order.

Have you ever seen it happen? I'm starting to wonder if it's just me.

[Iranon]

Do you have mixed weaponry, some of which has a range of 30k and some of 50k?
If not, is there anything else in play that may limit fire range to those values?