heat insulation spacers advice please

Hi All
Just a quickie!!. My Norton was fitted with 3mm thick heat insulation spacers between the carb manifold and cylinder head. Any reasons why I cannot fit 6mm spacers instead? Reason being the thicker ones were set to me in error :roll: .
Thanks

Can't think why it would matter engine-operation wise. If you use the oem airbox it could make fitting the filter a bit of a PITA since there's not a lot of clearance there anyway.