Hi Sugan,
I am not sure. I have tested a couple of years ago and tried to find documentation without any luck.
Let me correct my previous explanation:
When you use Horizon for lot for lot, suppose you enter 50 days.. during those 50 days your lot size is Lot for Lot (lot size EX).. This overwrite what you have in the Lot Size for Short Term Period.
Once the first 50 days are gone, the system will use the lot size entered in the Block: "Lot size for the long-term period".
Kind Regards,
Mariano