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

'''Author- Akshit Monga'''
from sys import stdin,stdout
# input = stdin.readline
t=int(input())
for _ in range(t):
    n=int(input())
    arr=[int(x) for x in input().split()]
    if len(set(arr))==1:
        print(-1)
        continue
    m=max(arr)
    p=-1
    for i in range(n):
        if arr[i]==m:
            if (i-1>=0 and arr[i-1]<m) or (i+1<=n-1 and arr[i+1]<m):
                p=i+1
                break
    print(p)