SCs inability with tomatoes

I just never seem to have the yield from them that other people get. No matter what variety. I think I do everything right (obviously missing something). They’re planted in raised beds or very large pots (depending on variety) I try to give them space, I give the support, feed weekly after first flowers, I pinch out armpits. I talk nicely to them! But still a pitiful production. It might be the varieties I’m choosing, but they can’t all be under achievers, can they. I choose them in a very scientific manner…………..by the names     . 
For example Black Russian. Love that tom. But I get about 4 ripe and a few under sized green. Everyone else has ladened trusses. Same with buffalo horn, love that one too.

Varieties could be the issue. I find dark tomatoes like Black Russian need a hot summer to perform well, they don't really like overcast weather. Up there you must get less sunshine hours than further South so you probably need earlier varieties. If you're not getting many fruit it could also mean the flowers are not being pollinated, which could be due to high temperatures, low humidity or lack of airflow/bees. Tickling trusses can definitely improve fruit set indoors. I'm probably going to get some shade netting for the greenhouse next year as whenever we have a heatwave the greenhouse gets boiling hot and tomatoes just don't pollinate properly in that kind of heat.