1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1


    
for _ in range(int(input())):
    n=int(input())
    arr=list(map(int,input().split()))    
    m=max(arr)
    if len(set(arr))==1:
        print(-1)
    else:
        for i in range(n):
            if i==0:
                if arr[i]==m:
                    if  arr[i]>arr[i+1]:
                        print(i+1)
                        break
            elif i==n-1:
                if arr[i]==m:
                    if arr[i]>arr[i-1]:
                        print(i+1)
                        break
            elif arr[i]==m:
                if arr[i]>arr[i-1] or arr[i]>arr[i+1]:
                    print(i+1)
                    break
                
            
        
    