I don't have a copy of the St Issells tithe map to hand anymore - I gave mine away several years back. However, I noted on my transcript of the tithe award where the rough locations of each entry were.
Richard Griffiths was the tenant of the Picton Castle estate leasing 3 cottages with gardens close to Stepaside. My notes indicate that this was Plumtree Hall.
Interestingly a Jane Griffiths signed a lease with the Picton Castle estate on 10/1/1809 for the same at a rent of £4 p.a. for the term of three lives (ie the term equating to the longest surviving life). The three lives listed in the lease are Richard Griffiths, son aged 27; John Evans, grandson aged 5 and kinswoman Mary Griffiths aged 14. The lease also recorded that Jane was the daughter of Henry Griffiths. This lease is held at the National Library of Wales (NLW), in the Picton Castle collection ref. 1255.
There are copies of the tithe map at the National Archives in Kew, the Pembrokeshire Archives and also the NLW.
Jon