I am *not* an expert, but my understanding is that tithes were essentially a tax on the agricultural productivity of the land in a parish, rather than a tax which every individual had to pay. So farmers would be liable to pay tithes on his crops and dairy produce, livestock etc, but if the parish was small or the land was of poor quality for agricultural purposes, then the resulting tithes would not amount to much.

I may be quite wrong, but I don't think that a person running the village shop or engaged in non-agricultural production such as lace-making (a widespread activity in east Devonshire and west Dorset at the time) would be liable to pay tithes on their earnings. So Delaford could be quite populous but still not generate a large income from tithes for the rector.

The laws relating to tithes were very complex, and had become so tangled and subject to local disputes that in 1836 the Tithe Commutation Act was passed to reorganise the whole system.

The link below is to a page about tithes in Devonshire but is also relevant to the rest of the country.