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

import sys
input = sys.stdin.readline

for _ in range(int(input())):
    n = int(input())
    # u,v = map(int,input().split())
    l = list(map(int,input().split()))
    
    if len(set(l)) == 1:
        print(-1)
    else:

        m = max(l)
        idx = -1
        for i in range(n):
            if l[i] == m:
                if i == 0:
                    if l[i+1] < m:
                        idx = i+1
                        break
                elif i == n-1:
                    if l[i-1] < m:
                        idx = i+1
                        break
                else:
                    if l[i+1] < m or l[i-1] < m:
                        idx = i+1
                        break

        print(idx)

