Due to roller big ends, lubrication depends on volume rather than pressure, oil pressure is around 10-15psi when cold and only around 5psi warm, so excess pressure wouldn't be the problem. The filtering material is concertinad screening around most of the filtering area From memory, I think the section nearest the gearbox internals has straight screening, so,, as it isn't afforded the extra strength of concertinad screening, perhaps the gears flinging oil around is the problem, but I doubt that very much. My guess would be the higher viscosity of cold oil, coupled with the slightly higher presure when cold.
Interestingly not all owners report problems with sump filters tearing???