I've revised my 'opinion' somewhat (now I've looked it up, rather than half-remembered

), and I think 2:1 would be fine, but they would be the smallest royal Regt on the field.
Going from the guesstimate by Chris Scott in his (excellent) 'The Armies and Uniforms of the Monmouth Rebellion'. His approximations for Dumbarton's (or more properly, The Royal Regiment of Foot) for Sedgemoor are;
5 coys = 86 Shot, 68 Pike & 50 Grenadiers.
I don't remember where I read it (maybe the same book), but with a bit of research you could probably justify having bagpiper or two