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())
    x = list(map(int,input().split(" ")))
    
    maximum = sorted(x)[-1]
    y = -1
    
    if len(set(x)) > 1:
        for i in range(n-1):
            if x[i] == maximum > x[i+1]:
                y = i
                break
            
        if y == -1:
            for j in range(n-1,0,-1):
                if x[j] == maximum > x[j-1]:
                    y = j
                    break
        print(y + 1)
    else:
        print(-1)