Multi shot production

[Spirited]

Hi folks

We're looking at multi shot production of gin on the smaller of our stills. My understanding is that for a x2 concentration multishot you would add twice the amount of botanicals to your standard charge (say 100 litres at 50% ABV). Once the new make spirit is collected this is diluted down with more alcohol before proofing to bottling strength.
My instinct tells me that if the total spirit collected from our still was say 40 litres at 75% then we would add a further 30 litres of alcohol before proofing (40/100 x 75). Could anyone elaborate/confirm/deny. we are aware of other issue such as proportional scaling of ingredients etc. Any advice would be appreciated.

Cheers - a cold distiller hugging his still to stay warm!