Mr G ... do you live at Planet Thanet ?
Ha ha ha!
It all started as an anti-blight experiment several years ago, Auntie.
The main idea is that if we grow toms in several locations around the house (and also used to on 'The Patch', but not now), and also in the GH, If blight is flying around in one part of the garden, then it may well avoid another section!
Over the years, we've been proved pretty-well correct, with some toms getting hit, and others not touched at all - the GH ones usually being the last to get affected, and that was well after the season had peaked. In fact, last year's best crop came from a shaded front tray of five plants, which only got the early morning sun, and avoided the afternoon heat we had in late summer.
We also try to stick to standard varieties. This year it's 'Sungold', 'Shirley', 'San Marzano' and some own seed from a 'Mountain Magic' tom given to me by a chum two years ago. While we love the flavour and texture of Heritage toms, they aren't as prolific as 'workhorse' varieties, so we tend to stay away from them now!
19 in pots and trays in the GH,
16 in pots and trays in front of the conservatory which get about seven hours sun,
16 in pots and trays in the shaded East-facing area as above, slightly shaded from lunchtime onwards.
All areas get a jumble of varieties. No favouritism, no special cases, no victims, plenty of encouragement, a "'Morning Chaps" welcome every day and lots of 'Tomorite' etc...:0)