Can the radials on a ground plane be horizontal if a 1:1 balun is used?
You might need a choke or a balun with horizontal radials and the match will likely not be too good either. It might show a better match than it really is using a long feed line however.
This will solve your radials close to the roof problem. An A99 without radials will probably work better being low to the Earth. Again you need to get the antenna above the peak of you roof.
Height is might with a 1/4 wave GP antenna.
I find that mounted down low and with horizontal radials on a 1/4 wave GP you might get more current on the radials that don't radiate well, and get less current on the radiator where you need the current.