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=[int(x) for x in input().split()]
    ans=-1
    maxi=max(arr)
    for i in range(n):
        if i==0 and arr[i]==maxi:
            if arr[i+1]<maxi:
                ans=i+1
                break
        elif i==n-1 and arr[i]==maxi:
            if arr[i-1]<maxi:
                ans=i+1
                break
        elif arr[i]==maxi:
            if arr[i]>arr[i-1] or arr[i]>arr[i+1]:
                ans=i+1
                break
    print(ans)