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
import math
def get_array(): return list(map(int, sys.stdin.readline().strip().split()))
def get_ints(): return map(int, sys.stdin.readline().strip().split())
def input(): return sys.stdin.readline().strip()
for _ in range(int(input())):
    n=int(input())
    a=get_array()
    if len(set(a))==1:
        print(-1)
    else:
        flag=0
        ans=0
        m=max(a)
        for i in range(n):
            if a[i]==m:
                if i+1<n:
                    if a[i+1]<a[i]:
                        flag=1
                        ans=i
                        break
                else:
                    if a[i-1]<a[i]:
                        flag=1
                        ans=i
                        break
        print(ans+1)