Baroque Ornamentation - Grace Notes

[Mandera3]

I know that in Baroque music that sometimes when you have a graces note followed by an 8th and 2 16ths, that you play it more like 4 16ths.

How do you know how the grace note should be played?

For example, I am playing a piece by Touchmoulin, and there are running 16th note triplets, and in the middle of the passage, there is a grace note before one of the groups.

Do I play this as 4 16th notes, or play it like a modern day grace-note, into 3 triplets?