2685, do as 385 suggests and work with the GP radial element for your tune.
You need to keep the radiator showing a bit of capacitance and adding a 6" spacer or a spring is probably not going to be of much benefit in this setup. If you get it close to tune you should be able to make it resonant right in the middle of 11 meters with a typical 102" whip. I get much better tuning response working with the GP radial length and their being a little longer is better up to a point.
The more radials the better, but if you can use at least three 1/4 wave electrical length elements in the GP you should get it to work fine.
You can also affect the match some by adjusting the angle. I have found 45 is a very good compromise angle. Personally I prefer to work my 1/4 wave with a bit of mismatch and have the GP more in the horizontal, I get more gain on my field strength meter. However if you want a really good match, start out at 45 degree down from vertical. You may see less gain, but your match will be better and your bandwidth should also improve.
If you feel the need to try and tune this one to a more perfect SWR, then try moving the angle of the GP up or down if you are able to do that. I find lowering the angle down tends to raise the 50 ohm resistive match closer to 50 ohms at the feed point and raising it up towards the horzontal does the opposite.
Good luck, you will find this antenna is pretty remarkable the way it will perform if you can get it up about 40+ feet.
