Womp womp. Well that sucks...

 

Instead, I think the antenna extension needs to be placed somewhere inside the car.

 

I'm inclined to agree, I also very much prefer the idea of increasing the power of the receiver, not the power of the sender. I've heard that in D2s, the receiver is in the headliner just forward of the rear sunroof. Can anyone confirm that this is where it is in a D1 as well?

 

 

The higher the remote the greater the range. The receiver may be in the headliner or mounted up high.
Anyone know what it looks like?

 

There is nothing like that in the DI. You have the alarm module located under the dash behind the glove box. There is an antenna wire that runs from that module up the right a pillar behind the interior a pillar with the speaker in it (obviously if you have an older DI there won't be a speaker in the interior a pillar cover). That's the antenna for the alarm module.