Merits will increase TP gained by 30 with each merit upgrade, up to a maximum of an additional 150 TP. This additional TP is granted whenever Reverse Flourish is used, and the amount of Finishing Moves consumed has no bearing on this amount.
TP returned from finishing moves is calculated by:
9.5*[FMs] + [Squared term multiplier]*[FMs]^2 + 3*[Number of RF merits]
Without either Charis Bangles, the Squared term multiplier is 0.5.