I've been away from computers for a few days.
Fara, you don't know me. I don't know you. I do, however, know Raghu.
As a newcomer to this activity, you may not be aware of the tests we conducted at Bensen Days a number of years ago on the airspeed actually experienced by gyro horizontal stabilizers. I designed the experiment, and got several of the guys to lend us gyros and help with testing and recording. I contributed an article detailing the setup, and our results, to the PRA magazine (back when there was one).
The highest airspeed over the H-stab is located at about the 2/3 prop radius point. This airspeed, in a full-throttle static test, varies from a low of about 80 mph for a slow-flying Gyrobee, to over 100 mph for a faster gyro such as an RAF or powerful MAC-powered Bensen.
The propwash tapers down from the full prop diameter, right at the prop, to about this 2/3 diameter by the time it reaches the H-stab; the exact amount of taper is a function of the ratio of slipstream to freestream speed (the taper is less at higher gyro airspeeds and greater at low ones). Especially on gyros with bulky components mounted on the engine block near the prop, there is a significant central "dead air" cone inside the propwash.
Certainly not after that test, but even before it, I would not, did not, and do not demand that a H-stab be centered on the prop hub. If it is to counteract HTL, however, it shouldn't be a full prop radius away from that center, either, because of the tapering effect I just mentioned. At a full prop diameter, the slipstream speed over the HS is little more than the freestream speed. Look up my article for numbers on the three gyro models we tested.
Despite the "dead air" zone, there's an advantage to placing the H-stab near the center of the slipstream, however. A more-or-less centered airfoil can be used to counteract the reaction torque created by the prop, which can roll a gyro in a zero G situation. Cierva developed this technique. Watch the (rare, but they exist) films of gyro PPO's, and you'll notice the craft executes a combined pitchover and rollover. Prop torque is over 100 ft.-lb. at full throttle in even in a small gyro with a redrive. Rolling to inverted is no healthier than pitching to inverted.
No, I do not posit that a heavy, high-powered gyro will need a continuous 600 lb. of thrust to stay airborne. PPO's, however, very frequently occur on climbout or coming out of a climbing pattern turn. In those flight regimes, the gyro will indeed be operating at full throttle at modest airspeed and the HS down-load needed to counteract the PPO moment will be as I described it. It's a significant phantom weight to carry unless you have a 15-foot tail boom.
I don't know the thrustline offset of a Magni; there are none in my part of the country. Based on gyros that I have measured, however, and on test figures given me by people I trust, unless the rotor is extraordinarily heavy or there something else heavy at the top of the mast, a gyro's prop thrustline needs to be at or below the crew's navel(s) for the gyro to be non-HTL. 1-2 inches of HTL is fairly easy to compensate for, however, with a properly designed H-stab.
I devised the "double hang test" in the early 90's to check the thustline location of my lowrider 503 DC Air Command. The test is based on a grade-school science-fair experiment. My gyro's prop thrustline came out about 5-6" above the CoM. This explained a lot of things that had mystified (and worried) me about this gyro's behavior. Adding the stock A.C. H-stab (located down at the 2/3 prop radius point where that good fast air is found) went a long way toward taming this gyro. Again, though, it does not neutralize the roll torque problem, and it may not be adequate to compensate fully for the PPO moment of a 532 engine and and added body pod.
A relatively slow, heavy and overbalanced rotor has a higher level of rotor damping than a light, fast one such as a Bensen rotor. This effect helps to provides a margin of safety against PPO in otherwise vulnerable gyros. I would not choose to depend on it, however.