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
from collections import Counter
t = int(input())
for _ in range(t):
    n = int(input())
    a = list(map(int,input().split()))
    if len(Counter(a).items()) == 1:
        print(-1)
        continue
    nax = max(a)
    ind = []
    for i in range(n):
        if a[i] == nax:
            ind.append(i+1)
    a.insert(0,a[0])
    a.append(a[n-1])
    flag = False
    ans = 0
    for i in range(len(ind)):
        if a[ind[i]] == a[ind[i]-1] and a[ind[i]] == a[ind[i]+1]:
            pass
        else:
            flag = True
            ans = ind[i]
            break
    print(ans)



