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()]
    if(len(set(arr)) == 1):
        print(-1)
    else:
        Max = max(arr)
        ok = False
        for i in range(n):
            if(arr[i] == Max):
                if(i == 0):
                    if(arr[i+1]<Max):
                        index = i+1
                        ok =True
                        break
                elif(i == n-1):
                    if(arr[i-1]<Max):
                        index = i + 1
                        ok =True
                        break
                else:
                    if(arr[i - 1] < Max or arr[i+1]<Max ):
                        index = i+1
                        ok = True
                        break
        if(ok):
            print(index)
        else:
            print(-1)