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It's only ever been an issue once in a tournament, where my 1/48 scale KV2 wouldn't quite fit over a bridge and my opponent wouldn't let me cross. All his vehicles were 1/56.
This is usually because people forget that 28mm model is on a 2mm tall base and your tank isn't....
Regarding the Perrys, my impression is that they deliberatedly started with using 1/56 scale as a reference for their WWII range, and sculpted their figures accordingly.
Also, the Perrys range included vehicles from quite an early stage (of their own design, in addition to the Blitzkrieg range that they retail), so they needed to consider the issue of the vehicle scale and infantry compatibility from quite an early stage.
Regarding the Perrys, my impression is that they deliberatedly started with using 1/56 scale as a reference for their WWII range, and sculpted their figures accordingly, even though this means that the figures in their WWII range are smaller than many of their other range - I think Captain Blood once posted a great reference picture showing Perry plastic figures from WWII and WotR ranges side by side.