I’m thinking the granny half step was abandoned for the majority of customers that want racing clusters and 8-9-10 clusters are now all the rage.
The key to half step is that the fractional difference between the chainrings should be half that of the freewheel cogs..with the chainrings close..4-5 teeth.
It also had something to do with deflection but cannot remember what it was..
I will use a 42-32-22 on the front and 14-28 on the back..sacks 7 speed.
I have the granny but not the half step..my first option is to get off and walk ..
Put it all together with BAR ENDS and you will be riding a knees SLED!!