Sum of part drag is smaller than total drag

[Reusables]

I have installed VOID and Editor Extensions Redux, but I'm fairly sure that they won't affect the craft performance while in flight.

Relevant KSP version is 1.3.1.

 

While modifying _Rade's propeller plane, I discovered that the drag is unusually high. (30kN~40kN of drag when the original plane usually gets under 15kN)

I thought it was because of some parts being exceptionally draggy, so I searched for the part. But I couldn't find any part which is particularly draggy.

For me it was strange, so I summed up the drag of the parts. Here's the results:

_______________________________________________________________

Central fuselage part (Cockpit ~ Central Nervs ) : 5.29kN

Side fuselages (Side Nervs & Aerodynamic cones) : 5.56kN

Wheels : 0.63kN

Side engines(Twitches) : 0.92kN

Wings : 3.07kN

All the other parts (which are in the fairing) : 0kN (Action menu says so; Some of them are part of another craft)

_______________________________________________________________

Total : 16.03kN

...What?

AFAIK the sum of part drag shown in the action menu should match with the total drag. Is this assumption wrong, or is this a bug?

If there's some aerodynamic effect causing this, I'd like to know.

 

Besides, here's the plane to test:

https://www.dropbox.com/s/0kak462rltk9zqo/Jastreb To Space.craft?dl=0

How to fly: Engage breaks, Press 0, press ']' once to switch craft and hold Alt+Q till it gets its full speed. Then press ']' again and hold Alt+E till it gets its full speed. Finally, press ']' again to back to the main craft and disengage breaks.

[OHara]

There is also the induced drag from the lift (the kinetic energy left in the down-wash of your wake, per unit length of wake) which is a separate entry 'L-I-D' in the aero-gui, just below your screenshot.  At low speeds, the lift-induced drag is relatively higher.  I think 'L-I-D' plus individual parts' drag adds to the displayed total.

[Reusables]

Thanks @OHara for good catch and letting me know that!

So it's because I either lack wings or speed, right? Then I'm going for more wings instead of trying to change other profiles. Again, thanks!