If you have your reasons for using a short cage, go for it. You seem to know what the deal is. Just don't lone it to your elderly father.
As far as your math as to what the smallest cog is you can use in the small ring... makes sense to me, though the chain wrap capacities Shimano states are usually conservative, so you will probably be able to use even smaller rings.
FWIW, nobody on the cares that you - or anyone else who says they are an engineer on the internet - are an engineer.
Last edited by Kapusta; 07-26-21 at 07:56 PM.