I gave up on the multi-city tool quite some time ago. When it was given a new look/freshen up it became utterly useless. The OP is doing well to see the first 6 flights of the day out of EDI. My home airport is GLA and the multi-city tool would generally show the first two or three flights of the day and that was it. The pricing it would throw up was also absolutely wild at times.

The “Create Custom Trip” option on BA.com is usually pretty good as showing all available flight options:

https://www.britishairways.com/badp/...ntryPoint=true

Although sometimes if it figures out you’re trying to book a simple return flight it’ll kick you back to the “Flight only” screen.

I’m not the most IT minded person however I’ve managed to install the ITA Matrix Power Tools mentioned above and have used them to force BA.com to allow me to book the flights and connections that suited me. BA.com seems to want to force you to book connecting times of between 75 and 120 minutes when flying from the regions, especially when the long haul destination is served by more than one flight a day.