A number of years ago, I visited BLR....not long after they certified their VG Kit. The owner discussed his kit with me, including the strakes, and their purpose.
He showed me video and photos of the tail of his wife's cub (the test airplane) taken in flight at high AOA. His purpose for installing the strakes was to reorganize the flow of air coming off the inboard end of the flaps at high AOA. In the stock configuration, with the horizontal tufted, the tufts closest to the fuselage were in very disturbed flow. In fact many of them were actually pointed forward at least part of the time.
He then experimented with blocking off that gap between the inboard end of the flap and the fuselage, by installing a (temporary) flap extension, which extended the flap to the fuselage. He flew that configuration with the tail tufted, and the disturbance to flow in that area was worse.
hence the strakes, which were intended to (and do) re-organize and smooth the disturbed air flow coming off the inboard end of the flaps as it flows over the inboard end of the horizontal stab, at high Alpha with flaps deployed.
Its been quite a few years, so my memory of the details is probably not great, but those images of the tufted tail in action were pretty dramatic.
MTV