[Antennas] Mobile: High Placed Loading Coil?

[DavidE Benedict]

Please, I need help with this proposed Rube Goldberg mobile antenna system.

QUESTION
I am wondering if, still using the Icom AH-4 tuner, if a coil of some
description part way up the 102 inch whip will enhance my radiation???

PROBLEM WHICH PROMPTS THE QUESTION
My new antenna  system does not do anywhere near as well as the
screwdriver antenna system.

HISTORY
I used to have a Henry Stewert Designs ScrewDriver antenna with my
Icom-706. 
It was great! 
It got out really well! 
But,... my car and antenna mount was crashed/crushed and I went to a
different antenna system.

PRESENT SYSTEM
-- Now I have a 102 inch whip on the roof rack on top of my station wagon.
---- I mounted the Icom AH-4 antenna tuner to the underside of my wagon's
roof interior (yes, it is all appropriately grounded).

------ There is only about a 4 or 5 inch wire between the tuner and the
whip which goes thru a 1-1/2 inch feed-thru in the auto's sheetmetal roof. 

THE QUESTION AGAIN
I am wondering if, still using the AH-4, a coil of some description part
way up the whip will enhance my radiation???

Any other suggestions?
(I want to keep and use the AH-4 in the system)