I was looking at avios availability for next year for a family of 3 using a premium plus voucher and get the following message. Does this mean the voucher only shows the additional seats if you book for two persons? I mistakenly thought it would open up more seats irrespective of number of persons.
"You won't see enhanced availability for this flight until you use one BA American Express Premium Plus Companion Voucher for every two travellers in this booking."

I can see 4 seats available when searching using the voucher then when I click through to book the option disappears and the msg above is shown