For example, if there is tightness in the low back, there is usually tightness in the lower legs so the spreading needle is applied on the lower legs to loosen up the low back. In my impression, it sometimes had opposite effect, that means low back became tighter after spreading needle on the lower legs. I think it was because that technique was applied to an area instead of a point so unnecessary part was also dispersed by tapping, leading to the opposite effect.
Since I started using Teishin (round-tip needle) for all treatment, I didn't use the spreading needle technique. However, when I started using the technique recently, I realized that it seemed effective to loosen up the tightness which was difficult to release only with tonification.
In Spreading Needle technique with Teishin, thicker side of Teishin where I usually hold (handle of the needle) is used for tapping like pediatric acupuncture. Strong tapping which is used with a regular needle seems not necessary. Light tapping seems good enough.