Some filters flow better than others (fact), and in the right circumstances (ie, cold starts with some revs & pump in pressure relief mode) a more restrictive filter can lower the engine's oil pressure some. Once the oil has warmed up and pump is out of relief mode, the more restrictive filter's effect on the engine oil pressure can't be seen.
There have been quite a few Vette owners who have seen this exact effect with a more restrictive filter - that is, less oil pressure during cold starts & warm-up phase as compared to when a less restrictive filter is used.