MR index calculating average with denormalized properties

I have a C# service that responds to clients periodically requesting an array of actions to perform and each action is stored in a RavenDB Action document with these properties where the last 2 properties are denormalized for performance:

• Id (String - PK)
• ClientId (String - FK)
• RequestId (String - Unique Id for the request. We don't store a Request entity)
• RequestDateTime (Date & Time - Date & time that request was made)
• RequestDuration (Time Span - How long the request took to determine the list of actions)

I want to create an MR index that provides hourly request statistics per client so that I can see statistics for Client #1, 01/02/22 09:00-10:00 etc. I'm struggling to calculate AvgRequestDuration because the group contains duplicate RequestDuration(s) due to the data being denormalized. Obviously min & max are not affected with duplicates.

public class Result
        {            
            public string ClientId { get; set; }
            public DateTime PeriodStart { get; set; }
            public TimeSpan MinRequestDuration { get; set; }
            public TimeSpan MaxRequestDuration { get; set; }
            public TimeSpan AvgRequestDuration { get; set; }
        }

        public ClientStatsByPeriodStartDateTime()
        {
            Map = action => from ac in actions
                                 let period = TimeSpan.FromHours(1)
                                 select new
                                 {                                                                    
                                     ClientId = ac.ClientId,
                                     PeriodStart = new DateTime(((ac.RequestDateTime.Ticks + period.Ticks - 1) / period.Ticks) * period.Ticks, DateTimeKind.Utc),
                                     ac.RequestDuration
                                 };

            Reduce = results => from result in results
                                group result by new
                                {                                    
                                    result.ClientId,
                                    result.PeriodStart
                                }

            into agg
                                select new
                                {
                                    ClientId = agg.Key.ClientId,
                                    PeriodStart = agg.Key.PeriodStart,
                                    AvgRequestDuration = agg.Avg(x => x.RequestDuration),   // This is wrong
                                    MinRequestDuration = agg.Min(x => x.RequestDuration),
                                    MaxRequestDuration = agg.Max(x => x.RequestDuration)
                                };
        }