Zuf
I”m not sure what your target yields as a grower are, but I got well over 3lb per tuber planted for Desiree maincrop in 2014 spacing them at 40 cm across a 1.5m bed and 50cm between rows. Far less than normal suggestions and the ‘earthing up’ was mostly done using comfrey leaves, grass mowings and a bit of soil on top. The ‘hills’ were much smaller than I’ve done before and no green potatoes emerged as a result.
Personally, I don’t see any logic in large distances between rows if your space between tubers within a row is only 40- 45cm. My experiment this summer shows that an even 40 – 45 cm space between tubers has no effect on yield per tuber and a consequent increase in yield/sq metre.
I guess, if space constraints aren’t your primary concern, you can afford to space things out more though……