Topband: shunt feeding the tower for 160m

[N2TK]

Well, I am going to start laying down ground radials to replace the 4
elevated radial system on my tower. Presently the shunt feed is 15' above
ground and matches fine. When I replace the elevated radials with ground
radials, should I move the feed point down closer to the ground? Is there
any advantage to doing that? If I should move it down, how far down should I
move it? Does it matter?
Presently I attach the shield of the coax to a tower leg at the feed point.
I also attach the shield of the coax at the base of the tower.
I have a coax switch and Comtek box attached to the tower at 4' above
ground. Do I want to keep the shunt feed above this to minimize any RF
getting into anything? Presently I have no RF problems with anything
attached to the tower.
With the feedline, is it recommended to add either ferrite cores or a single
layer of coax balun at the feedpoint?
Tnx for any feedback.
Tony
N2TK