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

for _ in range(int(input())):
    n = int(input())
    s = list(map(int,input().split()))
    if len(list(set(s))) == 1:
        print(-1)
        continue
    k = max(s)
    ans = -1
    for i in range(n):
        if s[i] == k:
            if i == 0:
                if s[i]>s[i+1]:
                    ans = i+1
                    break
            elif i == n-1:
                if s[i] > s[i-1]:
                    ans = i+1
                    break
            else:
                if s[i] > s[i+1] or s[i] > s[i-1]:
                    ans = i+1
                    break
    print(ans)
                
        
    

    
