this isn't making a lot of sense to me (at least the way I read your post) maybe I'm not understanding you or missing some info?
You "can barely receive" this desired station, yet the signal strength is either very good (7/9) or even max'd. What's the problem: is it noisy / distorted, sounds thin & weak, what's the deal?
What cable are you using: quad shield RG-6 coax is a preferred downlead. Do you have a 300 ohm to 75 ohm balum to match the 300 ohm antenna to the 75 ohm coax? Are your F-connectors crimped properly? Is the RF input of your tuners(s) properly impedance matched to the downlead (balnus there too if 300 ohm inputs - no balun if not). If the downlead is 300 ohm twinlead then you must keep it away from any metal along the route.
Grounding the antenna is not going to help anything so forget that.
Is the antenna fairly well aimed at your desired station? The mounting method I use is same as Cerrot: hang from the roof support beams using strong twine, and tie to the antenna crossmember, not to the elements. This way you may be able to swivel the antenna somewhat in order to best orient it and keep it above the wood.
Is the antenna itself in reasonable condition: elements not bent and the tie lines clear / not touching the crossmember? No broken insulators?
Because you apparently have a lot of signal strength you may indeed be able to use a smaller yagi. Have you tried any other tuners - borrow an auditon piece or have a friend bring theirs over and compare performance. Also take your tuner over to their house or to the dealership and compare that way.
Maybe you have so much gain that you are receiving co-channel from another station on the same freq? A variable gain tunable preselector may help; or a smaller gain yagi.
In my setup I use a Magnum Dynalab MD205 Signal Sleuth preselector preamp at the downstairs end. I have no preamp in the attic. Antenna is an older Radio Shack brand FM yagi(no idea how much gain or what model) it's been up there for over 30 years; it is about 28 feet above ground level. I am 60 miles out in deep fringe yet I receive very well. I've had a Dynaco FM5, then a Magnum Dynalab FT101, now a Magnum Dynalab MD102. All have worked very well with this setup.