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

"""
Code of Ayush Tiwari
Codeforces: servermonk
Codechef: ayush572000

"""
import sys
input = sys.stdin.buffer.readline

def solution():
    
    # This is the main code
    n=int(input())
    l=list(map(int,input().split()))
    m=max(l)
    for i in range(n):
        if l[i]==m:
            if i-1>=0 and l[i-1]<l[i]:
                print(i+1)
                return
            if i+1<n and l[i+1]<l[i]:
                print(i+1)
                return
    print(-1)
    
t=int(input())
for _ in range(t):
    solution()