Impale Can't Target Units Based Off SentryWard?

I made a unit based off sentry ward and i'm trying to get it to be impaled. but impale doesn't seem to notice it.. so i figured that i must change that unit to not have the classifications of "ward" so i changed it to 'ground' instead and it still doesnt' detect it.
I've compared that unit to other regular units and i see nothing different that would make impale treat my custom unit differently.. yet it does. what's going on here?

Why are you basing it off sentry ward? You could try another unit to base it off of. For example, if you need it to have timed life you could do it off of a water elemental or something. If you need the vision effect you could make an unmovable Shade.

Have you changed the Combat - Targeted As field? By defualt it is set to Ward.

yes, i've checked the classification and "targeted as" to make sure they match what the impale targets.

I did some tests by making another unit off of the sentry ward and i set it exactly the same and nothing.. then i changed the movement base speed to 1 and then it targetted that last created unit!... so that was weird.. then i tried it again with my other first custom unit that is almost identical and that doesn't work!! what the hell?!
it's based off the same unit.. the only differences between the two is the model and hitpoints. which should mean nothing.

Ah, i just ran a quick test. Due to the fact the game returns a specific "cannot impale this unit" error, rather than a generic "invalid target" type error i'm going to assume that Impale is hardcoded not to affect immobile units (ie those without the Move abilty Amov), for whatever reason

okay, i got the other figured out. was a friendly. lol. so conclusion is movespeed must be at least 1 for impale to work. go figure

If you set minimum move speed to zero in Gameplay Constants and add a custom movespeed reducing abilty (-100%) you should be able to circumvent most of the problems.

i'll have to try that out and see what happens, thax