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

from collections import *
import sys  
input=sys.stdin.readline

# "". join(strings)  
    
def ri():
    return int(input())
 
def rl():
    return list(map(int, input().split()))
    

t  = ri()

for _ in range(t):
    n = ri()
    aa = rl()
    maxi = max(aa)
    # print(maxi)
    ans = -2
    for i in range(n):
        if aa[i] == maxi:
            if i - 1 >= 0 and aa[i-1] < maxi:
                ans = i
                break
            if i + 1 <=  n - 1 and aa[i + 1] < maxi:
                ans = i
                break
    print(ans + 1)



