The multi-manager found that in two-thirds of IMA sectors funds below the average size were more likely to have outperformed consistently over the last three years.
What’s more, of the 313 funds across the IMA universe that had above-median performance in each of the three years observed, 61% were smaller than the average fund size in their sector.
Rob Burdett, co-head of Thames River Multi-Capital, said: "Overall the fact that smaller funds have done better is no surprise. Smaller funds can be more nimble, and such an attribute has perhaps been especially useful over the last three volatile years.
"Nevertheless there are some key exceptions among the likes of Adrian Frost and Adrian Gosden at Artemis Income, Richard Woolnough of M&G Strategic Bond, Cormac Weldon of Threadneedle American and the emerging markets team at the rightly ubiquitous Aberdeen and First State.
"They deserve to be highlighted but investors may consider blending with smaller funds to add value against these industry stalwarts."
The FundWatch Survey, looked at all 33 IMA sectors over three discrete one-year periods. It sought to identify the most consistent funds, based on those with above-average performance in all three periods.
Thames River releases this survey every quarter, but this time round also looked at fund size in relation to performance.
It said the picture varies from sector to sector but the outperformance of smaller funds was particularly noticeable in UK Equity Income – a sector that boasts some of the biggest funds.
In this sector eight out of nine funds that performed consistently above the median had below-median fund size, with Artemis Income the only "super-sized" fund in the group to receive the accolade.
The Active Managed, Asia Pacific, Global Bonds and UK All Companies sectors also saw significant outperformance by smaller funds compared to their larger counterparts.
