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

t=int(input())
for i in range(t):
    n=int(input())
    arr=[int(x) for x in input().split()]
    mx=0
    for j in arr:
        mx=max(mx,j)
    res=cnt=0
    for var in range(len(arr)):
        if arr[var]==mx:
            cnt=cnt+1
            if var==0:
                if arr[var+1]<arr[var]:
                    res=var
                    break
            elif var==len(arr)-1:
                if arr[var-1]<arr[var]:
                    res=var
                    break
            else:
                if arr[var-1]<arr[var] or arr[var+1]<arr[var]:
                    res=var
                    break
    if cnt!=n:
        print(res+1)
    else:
        print("-1") 
    
       
       
    