Thanks for the demonstration. Over the years, we have found this technique to tighten groups most of the time.
Of course, there are exceptions and many diehard springheads have found sandbagged forend positions with individual rifles that produce small groups. For example, with an old THeoben Gran Prix that I have owned since 1988 and know well, ragged one hole groups are possible at 50 yds by jamming the front of the trigger guard into a sand filled bag. However, the POI changes whenever I use that rifle with another hold in FT or the field. This change of POI is true for every springer that we have ever zeroed from the bench.
So, IMO, even if you have a good bench group, you are better off sighting in your springer from the palm so that it will be on target during normal shooting.