Hi James,
I know several commercial suppliers who state “no counterpoise needed” on their EFHWs and at QRP it’s no so bad but apart from the RF going where it shouldn’t the other point is that the counterpoise is the other half of the antenna and hence when using the coax feed as the counterpoise, it’s length and what it is close to will affect the tuning of the antenna.
I know it is not 100% true, but think of the driven element wire and the counterpoise as being like an off-centre-fed dipole and you’ll see how important the counterpoise or radials are. Even though this means half of the antenna is on the ground, the piece in the air has something to work against.
If you can add a separate counter-poise wire to the antenna, I would expect the signal reports that you receive will improve. This won’t solve your 17m band problem but it’ll put the complete antenna system in a better light. If you are limited on space to run out a counterpoise or radials, take a look at the “Loop on the ground” counterpoise system featured in RadCom a few months ago. For a small back yard that can be a good counterpoise for a vertical antenna.
73 Ed.