The second quarter Morningstar Professional Services Rankings Guide found that Brunswick dropped one client to 23, while Finsbury remained on 21.
Tulchan Communications was the big mover, gaining three FTSE 100 clients to reach 12.
In total, 25 agencies have FTSE clients, with only FTI Consulting and Maitland joining the top three with more than three clients.
FTI Consulting had the most listed clients overall - its 169 were almost double that of Buchanan (88) and Newgate Threadneedle's 83.
FTI had the most clients in the FTSE 250 and small-cap space, while Newgate Threadneedle pipped FTI in the AIM table by a single client.