Here is a quick test I did this morning for the Breen Frigate class design:
Name := Frigate Class
Design Type := Defense Ship
Vehicle Type := Ship
Default Strategy := Optimal Firing Range
Size Minimum Tonnage := 310
Size Maximum Tonnage := 330
Num Must Have At Least 1 Ability := 1
Must Have Ability 1 := Weapon
Minimum Speed := 2
Desired Speed := 2
Majority Weapon Family Pick 1 := 1
Majority Weapon Family Pick 2 := 25
Majority Weapon Family Pick 3 := 8
Majority Weapon Family Pick 4 := 2
Majority Weapon Family Pick 5 := 10
Secondary Weapon Family Pick 1 := 0
Secondary Weapon Family Pick 2 := 151
Secondary Weapon Family Pick 3 := 8
Secondary Weapon Family Pick 4 := 22
Secondary Weapon Family Pick 5 := 5
Shields Spaces Per One := 0
Armor Spaces Per One := 0
Majority Comp Spaces Per One := 200
Majority Comp Ability := Weapon
Secondary Comp Spaces Per One := 200
Secondary Comp Ability := Weapon
Num Misc Abilities := 12
Misc Ability 1 Name := AI Tag 02
Misc Ability 1 Spaces Per One := 50
Misc Ability 2 Name := Extra Movement Generation
Misc Ability 2 Spaces Per One := 10000
Misc Ability 3 Name := Combat Movement
Misc Ability 3 Spaces Per One := 100
Misc Ability 4 Name := Solar Supply Generation
Misc Ability 4 Spaces Per One := 50
Misc Ability 5 Name := Emergency Resupply
Misc Ability 5 Spaces Per One := 800
Misc Ability 6 Name := Armor Regeneration
Misc Ability 6 Spaces Per One := 100
Misc Ability 7 Name := Shield Generation
Misc Ability 7 Spaces Per One := 400
Misc Ability 8 Name := AI Tag 01
Misc Ability 8 Spaces Per One := 50
Misc Ability 9 Name := Combat To Hit Defense Plus
Misc Ability 9 Spaces Per One := 10000
Misc Ability 10 Name := Combat To Hit Offense Plus
Misc Ability 10 Spaces Per One := 10000
Misc Ability 11 Name := Multiplex Tracking
Misc Ability 11 Spaces Per One := 10000
Misc Ability 12 Name := Point-Defense
Misc Ability 12 Spaces Per One := 200
And the results:
You might be able to set the desired/min speed to 0, and then call for the nacelles themselves as another ability and place them with the warp core.
Anyway, the AI is adding extra scattering armor because it gives a better defense bonus than ecm components - hence why it is in the above design. If you fix up the ecm components - this shouldn't be a problem.