Hello,
this indeed depends on the foundry and will not be consistent for all. According to short channel effect when channel length getting smaller and small amount of charge will be created from drain and source diffusion, due to this Vth reduced. So smaller length smaller the vth. To combat this Vth reduction people use pocket hollows in the channel. Ideally this should make Vth flat across all the lengths but some time it might over compensate also, means Vth slightly increase with channel length up to some extent .

Thanks,
Raj.